I was asked to work part time for hourly basis on some work. What all should I be careful of?

Like the question mentions, what all should I know before getting into this?

• should I and the person sign a contract? If yes, who prepares the contract and what should be it's contents?
• should any specific clauses be defined?
• should I take up upfront fees?
• how to handle them validating work is done or not?
• should I not keep it hourly? Should I define the fees based on the work done?