Traditionally the first speech is from the father of the bride, followed by the groom and finally the best man. This is not set in stone and occasionally the bride likes to speak also.
Try to make the speech short and snappy. Get in a couple of funny anecdotes and personal stories you have experienced but overall keep it short and sweet.
Don't try making fun of people. It may seem funny to you but not to the person you are making fun of. Its ok to have a little bit of a laugh about funny situations but don't make it personal.
Most wedding speeches are designed to last 5–7 minutes, Try and memorise it if you can.
Try and include all the important people in your speech. The bride and groom for definite and also the bridesmaids and mother of the bride for definite.