Be simple.
Don't go too hardout on your first tileset. Make them just simple, but not that plain.
1Pixel lines are the best, really. Nothing too blocky.
Look up pixel art help too, and desgin some pixel things to just kinda get the first hang of it.
Dark outlines, lighter inside. This is usally good, depending on what you are making.
Take your time.
Hope it slightly helps.