Financing a flip, how should I do it?

[Fred Conway]

This would be my first deal of any kind, someone I know well and trust is looking for me to invest cash of about 25% of the purchase price into a fix and flip. Basically about 200k for the house, 30-50k in repairs and comps of 300k. What are some contingencies I should ask for? How would I write up a contract that basically I can't get screwed in the event something goes wrong? Should there be some type of clause that I get my money back as soon as the house is sold no matter what? Is there some kind of due diligence I should do before? How should I transfer the money? Check, bank transfer?

Basically, what are some basic things I should do?

Thanks