I´ve worked in restaurants a lot and started in wine tasting actually until I got tired of the snob and started with beer, the first advice that I can give you is train your nose first, forget about smoking and forget that you are smelling a beer, train your nose by smelling everything around, for wine there is even a few kits with essences that help you. Don´t be afraid of pointing aromas or flavours if you percive them NOBODY can tell that what your picking up it´s wrong or rigth. The easier aromas to pick up are the one that you been familiar with (specially the ones that you were exposed to since you were a little kid) and to start do not try to taste more than 3 or 4 beers after that it can get really confusing if you are not trained. Have a copy of the wheel of aromas and flavours on hand a keep tasting beers.
Easier thing it´s to percieve dryness or sweetness bu sure of that first, the are some excercices with glasses of water and differents amounts of sugar (same thing with citrics flavours differente glasses of water with different amounts of lemon juice for instance).
Remember there is some things that you have to have so previous notions: dyacetil is something that most homebrewers that I know can´t pick up in small doses, tannins on the other hand are easy (some dusty mouthfeel in your gums), just read read read and taste taste taste.