From Jo Querrien

In real life, we are all individuals.  We can be individuals in virtual worlds, too.  All it takes is being willing to experiment (and don't worry - you can always go back to the look you have now).  ALWAYS make a copy of anything other than a default item before modifying it!  Here are the basics:

A)  Every avatar MUST have shape, skin, eyes, and hair/eyebrow shaper.  ALL of them are things you can make yourself (with varying degrees of difficulty).

B)  Every avatar CAN have attachments and/or system clothing/tattoos, and alpha layers to disappear parts of the body. These are all also things you can make yourself (with varying degrees of difficulty).

C) An avatar can be saved in a folder to make it easy to "get dressed" or completely change your look.

1) The big four - your avatar MUST be wearing one (at a time) of each of these things.  If some inventory bug has caused you to somehow not be wearing any one (or wearing more than one of any) of them, you will be a blob of plasma (unrezzable).
    Shape - Your shape is the underlying architecture of your body. You can create a new shape in your inventory (Create --> new body part --> shape in Firestorm, other viewers are usually similar). The new shape will be "Ruth"'s shape, which is a very ugly female shape.  Yes, it's ugly, but think of it as something you really can't mess up.  And if you do somehow hate your experimental shape more than Ruth, you can always just delete it and make a new one. Creating a new shape is always free, so there's no reason not to. If you edit your new shape (either by right clicking it in inventory and choosing Edit or by right clicking yourself and choosing Appearance --> edit shape), you will see several tabs across the top, each with sliders below.  Most of them are self-explanatory (with one notable exception).  Play with them!  Remember that this is Ruth - you can't mess her up.  Move each slider around, and see what it does.  If you do not want to create a female shape, click the box at the top marked "male", and you will get an equally hideous male body.  The one slider that is NOT what it seems to be is Hip Width (in the Legs tab).  One might imagine that a slider called "Hip Width" would control...the width of the hips.  It does NOT.  It controls how far apart the legs are.  The actual hip width is controlled by the unfortunately named "Saddlebags" slider.
    Skin - Your skin is the paint that goes on top of the shape, to give it color, texture, and shading.  You can create a new skin in your inventory in a similar way as you create a new shape.  The default skin is also Ruth (or her male equivalent), and is just as awful as the default shape.  The skin editor does also have sliders that you can use to modify its tint, add freckles, etc, but there really isn't anything you can do to make it look truly human that way.  Fortunately, you can also bring in textures and apply them to the skin (the three squares at the top of the skin editing window, onto which you can drag pre-made textures).  Note that if you use textures rather than the default skin, none of the sliders will have any effect.  That is how the skins that don't look so bad are made. You can, if you are sufficiently skilled with graphics editing software, make your own skin, but it is a difficult process to make a good one, and well beyond the scope of this tutorial.  If you consider yourself highly skilled, please do make skins and add them to the variety available in your world - it is difficult to be truly unique without a good skin.  If you, like me, lack the ability to make your own skins, there should be a selection of options available in your world made by others who do have those skills. Note that a skin can have clothing or underwear painted on it.  If your skin is one of those, you cannot remove them without changing skins.  Note that changing the skin of an avatar can significantly change the look of the avatar.  If you change skins, you may find that you no longer have the look you want, and need to modify your shape accordingly.  That does not mean that the skin or the shape are not good, it merely means that the new skin is different from the old skin.
    Eyes - Your eyes are the paint that goes on top of the eyes of your avatar, to make them look like eyes.  You can create a new pair of eyes in your inventory using the same method as for shapes or skins.  The default eyes are considerably less hideous than the default skin and shape, and may even be suitable for your purposes. You can modify the tint and shade of these eyes with sliders in the eyes editor.  You can also drag a pre-made texture onto them, just as with the skins.  Pre-made textures can produce much more interesting eyes than the defaults (with light reflections and shadows on the whites so that they do not look flat).  As with skins, if you are using eyes that have their own texture rather than using the defaults, none of the sliders in the eye editing window will have any effect.
    Hair/eyebrow shaper - Originally, this was meant to be hair, but its limitations (plus the fact that it moves like it's made of chewing gum) quickly caused it to be replaced with hair attachments.  It is still referred to as hair in your inventory, so to create a new one, you would choose "New Hair" rather than "new eyebrow shaper".  Editing this brings up the hair editing window, which you can use to make the default hair disappear (by setting size to 0 and changing the texture to Transparent by clicking the box and choosing Transparent), and to edit the position and shape of the eyebrows (whether the skin is default or not).  For male avatars, this edit window also has a tab for editing the shape of facial hair.  These sliders will NOT add facial hair to a skin that does not have facial hair painted on, but they will change the shape of the face underneath where the nonexistent hair would be.  This allows some interesting chin shapes for male avatar chins if desired.

2) Optional additions - In addition to the four things you MUST wear, you can customize your avatar in a large number of ways.  This category includes everything from flexi hair and skirts to sculpted pants cuffs to entire avatars added on (the body underneath can be partially or completely hidden with an alpha).  ALL of these things can be made, some inworld via prim builds, some using external graphics programs (such as GIMP, Photoshop, or Blender), and some with a combination of the two.  The processes for actually making these things is well beyond the scope of this tutorial, but there are many tutorials and videos online that can be used to learn how to make whatever you want to make.
    - Make sure that you wear an item on an appropriate location. The creator should have set that up for you, but if you are the creator, or if they did not, you will need to do so.  If you wear something, and it shows up on your hand instead of where it should be, take it off, and re-attach it to the correct location.  This is done by right clicking it in inventory, and choosing Attach To from the menu, then choosing the appropriate location.  NOTE - some viewers, such as Firestorm, have attachment points that other viewers do not (base of tail, for instance).  Avoid these attachment points whenever possible.  If someone who is not using a viewer that has that attachment point sees you, there's no telling what they will see instead of the object being where it should be.
    - Note that the hands are rarely good places to attach things, because they are the default attachment point for anything that doesn't have a designated attachment point.  In Second Life, the Right Hand is the default, and in most other worlds, the Left Hand is the default.  If you are wearing anything on that hand when you wear something that goes to that hand (a box you are checking for contents, a glass of champagne you got from a dispenser at a party, or something you accidentally double clicked in your inventory), the thing you were wearing is replaced.
    - System layer items (with inventory icons that have various looks), including clothing, alphas, and tattoos, will automatically go to the correct location (and will neither take up an attachment point nor add render weight to your avatar).  They are also not able to contain scripts, making them excellent options for any place where lag is an issue and you do not wish to experience any more of it than you need to.
    - Wearing more than one thing in the same spot can be done (if your viewer allows it), but you must ADD rather than wear the item in order to do so.  That is true for wearing both a pair of glasses and a nose ring at the same time when both are attached to the nose as well as for wearing both a tattoo layer freckles and a tattoo layer tattoo or both an alpha to hide your feet so they don't stick out of a pair of shoes and an alpha to hide your eyelashes so they don't cause flickering with attachable eyelashes.
    - Objects (look like boxes in your inventory) can be edited to perfect their fit on your avatar (unless their creator made them no-modify or they are made of rigged mesh).  The size, shape, and position of the item (or of part of the item, as in moving a lock of hair so it doesn't poke through a hat) can all be edited if the object is modify.  Editing the position, size, or location of an item that you are wearing is done the same way editing an object on the ground is done.  Some creators put a script in their items that allows re-sizing all or part of the item even though the item itself is no-modify - if possible, once you have fitted such an item, make a copy of it, and delete the scripts from the copy that you will wear.  This will keep you from carrying around unnecessary scripts and the lag they cause.  Standing on a pose stand before editing attachments will prevent your avatar from moving while you are trying to edit things.  ALWAYS make a copy before editing any attachment!

3) Once you have the look you want for your avatar, make sure that everything you are wearing (or a copy of it) is in a folder with an appropriate name.  Once you have done that, you can put that avatar (complete with outfit) back on in the blink of an eye by right clicking the folder and choosing "Replace Current Outfit" from the list.  Having a folder with your current look in it is useful for many reasons:
    - The folder does NOT need to be in outfits (in fact, you can save inventory by NOT using the Outfits folder) in order to Replace Current Outfit and change back to your original look (assuming of course you got EVERYTHING from your original look into that folder - anything you left out won't be in there).
    - If you accidentally take off something by wearing something else in that location, you can quickly relocate it and put it back on if it is in the folder you expect it to be in, instead of having to look for it in some unrelated folder.
    - If a computer error forces you to do a character test (to un-plasma yourself, for instance), you are not stuck being Ruth for long when you can change back with a click of the mouse instead of having to hunt down all the various parts of yourself.

Last, but not least, remember that you are not limited to one look. You CAN have the same face, eyes, and hair all the time, and only change clothing (like in real life), but you can also have as many different avatars on your account as you like, and wear whoever you're in the mood for that day (note that if you are planning to change genders a lot, you might want to choose a name that is not gender specific).