Simply put, getting a "Pre-Approval" from a lender before you start looking at homes gives you more control over the home buying process, and is a sign to Sellers that you are a serious buyer. And, when you find the right home, you can make an offer right away, since you've already done the gathering of info for your lender, and you have a mutual understanding of the price range that you are approved for.
You'll need to collect at least two years of tax returns, several months of bank statements and pay stubs, any documents that show additional sources of income. It's a good idea to check your credit report to make things are in order, and address any errors.
Most lenders will process the pre-approval free of charge. Set yourself up for success, and talk to a local lender today, then let's go look at some houses and get you in your 2020 home!