[QUOTE]I was more curious about use of original sprites since I don't have the ability to make my own.[/QUOTE]


Here are a some useful pictures that point out things to pay attention to. They also illustrate some of the points I make below.

http://www.mediafire.com/file/mnjgym0igey/create_sprites.zip



I almost never make sprites completely from scratch.
Usually, I start with another game character, 
remove their hair & outfit, then build from there.
That makes things much easier since you don't have to figure out the new character's proportions, you'll simply re-use proportions that you already know will work.

If I need a completely new pose,
I figure out the approximate size of the head and
then draw each limb in a single color.
I add an outline, adjusting the body's shape as I go,
then add the character's head.
Finally, I'll add an outfit.

Paying attention to proportions is helpful even with small sprites like these.
The eyes should be centered on the head, unless it's tilted up or down.
And the size of the head compared to the body will generally be either 1/3 to 1/2 the size of the entire sprite.
This is because you need to be able to clearly see the character's eyes, which convey the most expression.

This is also why creating small sprites in 3D doesn't work too well, because the expression gets lost in the blurred pixels.
And at that size, you cannot afford the blurry or misplaced pixels you get from 3D. It's just not selective enough with details.

Of course, you want to use outlines.
Generally a darker version of the color you're outlining.

Be careful with dark shading, unless it's cloth, since it'll hide details. I usually keep the colors pretty bright.

You can re-use character bodies by swapping heads & changing outfits. Some sprite artists go even farther, but this has always been enough for me.

If you don't use translucent pixels, and limit the number of colors you use, you can compress the image as an 8-bit PNG, which takes less memory.

Never use anti-aliasing on the outside of the character's outline (unless you're using 24-bit PNG)
But you can still imitate anti-aliasing on the inside of the outlines by placing somewhat darker pixels at the corners of the outline when it tries to curve.
That way, the inner part of the outline looks a little smoother.
(you can see what I mean if you look at some of my characters)

Finally, when you create a walk animation for an RPG game character, you'll want one of the frames to be their standing pose. (like in RPG Maker games)
Then in the sprite settings, make sure their starting frame is that standing pose, because my RPG Maker defaults to that frame when a character stops walking.

When you edit sprites in Photoshop, you can display the same image twice at 2 different zoom levels. This is helpful for previewing how a sprite looks while you're editing it.
To do this, go to the top menu, and select:
 Window -> Arrange -> New window for ????
The choice (or choices) at the bottom will duplicate a window.
Duplicate windows update at the same time.
And Photoshop won remind you to save until you try to close the last one for a given file.