Do what you want to do. After an entire scarf of garter, I'll bet you've got that stitch figured out. Mittens and hats are good "step up" projects and they're small, so they are a quick reward.
socks. Some people like to practice new stitches by making wash cloths.
There are endless choices out there. You can look at the free patterns tab at the top of the page or you can go to an online magazine like www.knitty.com
to get new ideas.
Welcome to the forum!