This is the overview. Seriously, have an attorney draft this or review a draft of a contract that you choose to use. An attorney I know suggests that investors use the standard Residential Purchase Agreement that agents use. Probably available online. The details of the language is state specific and necessary to protect you. I'm just giving a brief rundown here.
1. Put it under contract with seller. I put $500 down with language that says something to effect that if buyer (me) can't buy, then that is full liquidated damages. Meaning, seller can't sue for specific performance or get any more than that.
2. To be held at title company of buyers choice. I put no time provision for me to drop off this deposit. Since many deals are off-market, there is no real estate broker.
3. I put in a 30 day (business days, excluding holidays) due diligence period. If sellers want to ask for less, then they can. Allow yourself plenty of time.
4. Somewhere in the document, you should have assignment language. It's like "...contract may be assigned...blah blah about enuring to benefit of heirs, successors, assigns..." Don't make a big deal of this. It's standard stuff and I've never had a seller ask me about it. Just because you know you plan to assign it, doesn't mean they know (or care).
Wholesaling doesn't mean that you HAVE to assign it. I don't do it that way because I don't want my buyers to see how much money I'm making. There are many transactional funding companies who will loan you the money, once you have a buyer under contract.