Talk with some local Community Banks, they have different lending standards as often they keep their loans in-house and do not have to comply with the Fannie Mae guide lines. I have done multiple loans with Community banks with fantastic terms. Also consider owner financing. If you can get owner financing from the seller there is no need to wait for your 'pre-approval' Realtors want you to wait so you don't waste their time driving you around. Go out and look for your own properties without the realtor you may find properties for sale by owner with owner financing. I purchased a 10 Unit apartment building outside of Charleston WV about 3 weeks ago. I got the owner to carry a second mortgage for 20% of the purchase at 5% interest. I got a community bank that would loan up to 85% of the purchase to provide me the rest of funds. I walked away with about 1400.00 at closing with putting no money into the deal at all. Essentially I got paid 1400.00 to purchase the property! The property cash flows and has room for improvements in NOI. As a bonus my wife got her Realtors license only to use on investment deals we do, since she was the realtor on this transaction she got another 5700.00 of commission at close that we put back into the company so effectively we got 7100.00 to purchase a property with cash flow!
Read and learn all you can but don't believe anyone who says this is the way it must be done or it can only be done this way. If you find the right deal and simply ask for what you want you will be amazed at what you can do.
Good Luck!