Those few moments while you are making the toast are yours. Do not wait till the last minute to write down your thoughts because then your speech will get all jumbled up. The toast should be crisp, personal and sweet. Adding a little humour is preferable, so you can, if you think a little funny statement can fit in your time slot. Your toast should definitely not make the couple or the audiences feel awkward at any point.
Practice indeed makes a man perfect. After you are done writing down all the things that you have to say, you should practice your speech. It is better that you stand in front of a mirror and look at yourself while giving your speech. You can improve your body language this way as well. Imagine the audience is sitting right in front of you, grab a glass from the kitchen and rehearse to make it seem as if you are giving an actual speech. The more you practice, better are the chances that you will not stutter while giving your actual speech.
On the day you have to give your speech, make sure that your nerves are under control. Keep your anxiety levels in check. Do not rush for your turn, let the others speak first, and when you feel ready and all set to give your speech, steal the show.
Start your speech by introducing yourself first., If you do not introduce yourself properly and your relation to the bride or the groom, then there are chances that people will not be able to relate to what you are saying. Make sure that people know where you are coming from.
Always keep a smile on your face. This is definitely not the occasion to complain, concentrate on all the good things about the couple and your relationship with them.