Not sure what kind of a debate you are going to have, but in school we have two kinds- extempore and the debates where you are made known the topic a week in advance. For the last six years, I have been a regular participant in the latter.
Now, what my experience has taught me:
1.If you have a debate a week ahead, practice everyday that week for two hours.
2. First begin by reading through the material a few times. Do the initial work, enunciate any meanings that are unclear, get all pronounciations right.
3.Now, you got to learn.
4.When you practice, keep a bottle by hand and practice non-stop, if the debate is timed, use a stop watch.
5.A day before.....Relax, breathe deeply
6.Record your debate in audio form, play it and see where you get voice modifications wrong.
7.When you plunge into bed, for a nights nap, recite the whole speech out in your mind.
8.Visualize
Do your best!