since you already took a puppy class, why not continue on in some basic obedience classes? I took my dog through levels 1, 2, and 3 (advanced). it's great socializing and you work on skills such as drop/leave it extensively.
drop it/leave it are 2 commands which took TIME to work on. In the classes I took, we started w/ an item (crumpled paper towel, toy, shoe, etc...) in center of room. walked dog on leash up to the item, when he showed interest, say LEAVE IT (firm tone) and guide the pup away from the item. when he takes his focus off it, treat/reward! leave it is something that should be practiced ALOT. on walks, in the house, every time you get a chance - reinforce it. always praise/treat when your dog succeeds, and she'll get soon enough.
I worked on DROP IT anytime I played w/ my dog. he got the ball, DROP IT, if he dropped it, I threw it again! more play was the reward.