My approach is really to think about the kind of organisms you want to cover for. For instance, if you suspect an oral flora, you want to make sure you want to cover anaerobic organisms. The two atbxs that are commonly used for this purpose are metronidazole and clindamycin. I found that for step 3, the things are tested the most aren't necessarily the choice of antibiotics, but rather their side effects.
Memorizing a list is good,but understanding each antibiotic's coverage and the most common organism underlying the infection are what's going to make that list sticks in your head.
