The running order of speeches at a wedding is really important, and something that is frequently overlooked. Where you sit in the line up of speakers dictates what you should be saying, how you open the speech, and also how long your speech should be. And this is why so many best man speeches get it wrong right from the kick off.
The best man speech generally comes at the very end of the proceedings, and this is so important to remember when it comes to the start of your speech. So, before you speak the father of the bride has welcomed and thanked everyone, the groom has welcomed and thanked everyone, and chances are these days that so have the bridesmaids and mother of the groom. This is just really poor planning. A succession of people standing up and saying exactly the same thing is completely pointless and counterproductive. The last thing a best man should do is begin his speech by thanking and welcoming everyone - not only has that been extensively covered, but it's also not your wedding.
A great best man speech should start with a simple introduction and then into the story of the groom. However, if you are making this speech in Australia things are a little different. The groom speaks last at an Australian wedding, and for some reason this is creeping in a little to UK weddings as well. There's nothing wrong with that at all, but it will affect the way you reference the groom if he hasn't spoken yet, so make sure you know where you sit. Also I alluded earlier to the number of speakers, and this is crucial. These days, especially in the US, multiple speakers are the growing norm, and that affects a best man more than anyone. If you are a best man making your speech after 5 people have made theirs, then you're already on borrowed time. The guests are well past their attention span deficit reserves and want to get on with things, so you have got to be really efficient and on the money. There's no time for rambling introductions, lengthy stories and endless anecdotes. This is what American best men are really good at: short, effective and powerful speeches that do what they do in the most efficient way. Make everything count, avoid repetition and keep an eye on the time.
For every extra speaker above the Nato standard of father of the bride/groom/best man, I would knock off at least 30 seconds to your speech, maybe more. If you are two best men, then you really have to reign things in, particularly in you're making separare best man speeches. The hardest position to find yourself in is the last best man speaking following another best man speech. If the other guy was really funny, you're toast; if the other guy was awful then the guests have already had enough. So, speak to the groom, find out where you sit in the order of speakers and use that information to make your best man speech the best it can be.