I love mendeley. I wish I'd used it all through my PhD rather than just the last bits.
I've made a folder that the program scans so I just drop everything I have in there and it picks it up. It acts as a backup for all my files too.
I don't think theres much that can be given in the way of tips. It's fairly simple and skipped most of the instructions. All I would say is that when your collection starts to get on the large side then it's time to start organising lists with the function. I've got one for my general area, sub topics with in it, a couple of other area's I'm interested and then lists for those that would be useful for teaching.