For an exam that asks you to compare multiple anthology texts, it's best to revise a selection of sources by theme, so that in the exam you can think of an answer- and how to support it- quickly, regardless of the question. For poetry, sources which make an impression on you personally, for their emotional impact or narrative, are a good place to start, as you're more likely to remember them even under exam pressure. Learn a handful of poems with a broad and balanced range of themes so you can construct an answer quickly, then draw on additional sources if they're particularly relevant to the question, or if you need more evidence.