Things to remember in photoshop:
Check to be sure your magic wand and paint bucket filler tools are not using anti-alias selective ability, and set the threshold for their fill/selecting to 0. This should save you some grief with doing fills and selects.
These are great linearts and you're getting the idea with shading on your second work. Like it was mentioned, just surf around the site for inspiration if you need any, and keep on going, since you have great promise! Welcome to Pixelation!!