well as a fairly experienced debater, and musician (believe it or not it has relevance) i'd have to say:
a) the 1st line of your speech is the most important one. make it confronting so as to get the attention of your audience. this will also make you feel more confident, if you can deliver your 1st line with panache and see the audience respond, it makes the rest of the speech a whole lot easier.
b) do NOT plan your hand gestures. seriously, dont. just do whatever feels natural with hand motion to emphasise each point. with other movements, dont pace, but u can wander a little from your starting point, unless you're behind a lectern in which case stay put. imo lecterns are bad, if you have a choice ditch it. you can turn to address different parts of the audience, as long as you never have your back to anyone. basically, whatever you do, make sure that the gestures are never the primary "focus" of the speech - ppl should be listening to what you say without being too distracted by what your hands are doing.
c) memorising your speech is good, but not necessary; dont waste time doing that as opposed to improving the content. as you write and edit it you'll become familiar enough with the matter that you wont need to read, and just use prompt cards which have the key points of your speech written in point form, 1 to a card, and possibly the linking sentence.
d) basically, what you want to do is have good "presence" - giving a speech (or an oral
) is a performance, you have to perform for the audience, and the best way to do this is to be supremely confident but without being arrogant bcos then you get sloppy.
e) this is the most important part: HAVE FUN! if you arent enjoying yourself, the audience WILL notice, and they'll respond by not having fun themselves.
good luck!
sam.