This may seem obvious, but it's worth stating. For an immediate lesson in what makes great advertising, pick up the latest issue of Communication Arts. In fact, pick up any past issue of CA.
I received my Advertising Annual #49 yesterday and practically pet it in excitement. That is, after I swatted away 4 creatives who also wanted to have a look. It has to be one the most succinct collections of great work in one place. (I'll throw in the obligatory "in my opinion" for those who may disagree).
For any student of advertising or entry-level creative, this is a must-read primer. Even I oohhhed and aahhhed at most of the work in there. My bet is if you studied the last 10 years of Advertising Annuals you'd learn more than your first year in the business. The work you see is just plain great (with the exception of those Amex ads - not really in agreement with their multiple wins, sorry). Anyway, pick it up and have a look. It is, and will continue to be, a great textbook of the best advertising work.