Hi Shane,
First step is to make contact with the homeowner in pre-foreclosure. Are these leads coming to you from a source that has a foot in the door...or are they just addresses and mortgage balances?
Let's look over the BK for now just to simplify.
You will need a purchase contract, letter of authorization, and proof of funds letter for starters. The letter of authorization is what gives you the authority to speak to the lender on behalf of the borrower.
What you want is to make contact with the foreclosing lender, fax in the auth letter and find out what sort of short sale package they require to you put together, if any.
Once you get the package submitted, your next step is to get the bank to order an interior BPO (Broker Price Opinion.) This is where an agent, hired by the bank, meets you at the house and valuates if for the bank. You want this value to come in as low as possible...so meet them at the house and point out everything that could possibly de-value the property. There are a lot of strategies here.
Once that value gets back to the bank...they will compare it to your offer, along with comparable sales that the BPO agent also submits...they will accept, reject, counter.
This is an overview.