When producing your best man speech here are a couple different things you should look at once you write your speech.
1) You were picked as the best man - Don't forget that you were selected as the best man from all the other possible people, consequently make sure you make an effort to appropriately write a good speech. Never rush your speech, try your best to give yourself plenty of time to write it. It is not likely ideal to get it done in a single sitting, allow yourself some time to think of the stories in which you may wish to share within your speech.
2) Aim to keep it brief - Try not to ramble on and turn it into a long and detailed speech. A good best man speech is ordinarily just 5-10 minutes long. Do not forget, the bar is shut down during your speech, consequently people would like it to be over as fast as possible, I know that might be a little severe however people will become unfocused if your speech is too long.
3) Make clear how you know the bride and groom - Even if your the brother still clarify who you are and how you know the bride and groom. Most of the bridges family and friends probably will not know who you are so let them know.
4) Tell a story regarding both the bride and groom - The story that will go over the best is one that is embarrassing for the groom and where the bride comes to the rescue and takes care of the groom.
5) Say thanks to the parents - Make sure to thank both sides of the family, most likely the brides mother and father finance the , if that is the case don't say "thank you for paying for the wedding" say something along the lines of "thank you Mr. and Mrs. Jones for making this all possible, this is a very special day and we are all grateful to be here to share this moment with (bride and grooms name).
6) Best wishes to the bride and groom - Make sure that you wish them the best and wish they have happy, long, and wholesome marriage together. Give thanks the groom and let him know how happy and grateful you are to be the best man.
7) Raise a toast - Raise your glass and let us celebrate this wonderful day!