What @djsmiley2k said.
1/ Be more formal
2/ Think of the elevator pitch (you have 30s to describe what you want), so put that first, then justify it.
3/ "Dear Mr blah" (more formal than "Hey pal", I'm looking for $$ sponsorship for foo.
4/ Explain foo. Ask for explicit $$ and breakdown cost. Then ask him to contribute what he can. Explain what **he** can get for his for his contribution (free publicity for his $company?)
5/ Finish with Yours faithfully or Yours sincerely"