(Largely inspired by a conversation with
sunavatar, who will disagree with most or all of this.)
1. Meter is the mother, meter is the father, all good things come from meter. Free verse = anathema. Also, if you're using rhyme (which is fun but makes life more difficult), a complex rhyme scheme with relatively few rhymes is good.
2. Parallelism and repetition are fun. Don't overuse them, but they are ultimately a good thing.
3. You need space to actually, y'know, say things. Less than about eight lines is in a sort of limboish territory between poem and epigram, and closer to the latter. Not that I've anything against epigrams, but let's call a spade a spade here.
4. Imagery is important, and it's as much imagery of the words themselves floating up in front of me as it is imagery of what they depict. The sound has to be Right as well as the meaning.