I've written previously on how many academic conference presentations are (put mildly) somewhere between sleep-inducing and cringe-inducing.
This post at The Program lists an impressive collection of advice on how to do a better job at it. Of the ten pieces, I've only read a couple so far, but they're worth the time spent checking them out. Definitely read them before your next conference presentation.
BTW - the worst presentation was a job market presentation someone made at my school while I was still a grad student. It was a highly technical one - on option pricing. The candidate's slides consisted of page after page of calculations (with little intuition), and his transparencies were photocopies of hand-written notes ON LINED PAPER. What's more, they had obviously been done on a copy machine that was both running out of toner and was very, very much in need of a good cleaning.
In fairness, this was in the days before widespread use of presentation software. But really - for a job talk at a fairly respected research school, is it too much to ask that you wipe the glass on the copier off with some Windex?