...or, more accurately, What Not to Do when trying to creep someone at the library. (Come on now. I'm sure you've all done this. Or wanted to do this. Close enough...) No worries, I'm here to help!
1- Giggling is not subtle. No but really.
2- Hope that your target is sitting in a well-populated area... and not in the most awkward spot beside the dictionaries. I mean really, why sit there anyway? Don't you know that people might want to come... -coughcough- investigate you? Cut me some slack here.
3- If you want a subtle phone, do not get a Blackberry. I love my phone, but I must admit that the keys are a little loud, and therefore not conducive to silent stalking. (Or silent usage while in class. These are important things to keep in mind!) In this respect (and this respect only!) touch-screens are preferable.
4- Hope that your target is sitting near interesting books. The aforementioned dictionaries do not make for good 'Oh, yes, I'm fascinated by this book and I'm totally staring at it and not your head' material. Nor do books such as "Our Aging Problem: how to take care of your elderly parents" or "Fortune 500: the revised list!" Try to apply no. 1 while looking at those titles, I dare you. (To say nothing of the sex manuals that were also lying nearby... Yes, I am that immature.)
5- Have a friend nearby. This way, if all else fails, you can run up to them and pretend that you were looking for them The Entire Time. "Omg, you've lost so much weight that I thought you were hiding in the shelf!" Convincing, right?
...or you could just wait to run into the target while walking down the stairs. That also works.