What is the easiest way to get pre-approved?
Put in an application with a lender.
Talk to a lender. Usually you'll need to have a credit score above 620, the down payment requirement varies by occupancy, and stable income that is likely to continue
Contact a local mortgage broker who you can apply with. Have them explain how much you qualify for, why, and share scenarios with you from different price points.
@Josh Zeloyle along with what other's have shared and ensuring that you're finances are in order, I would recommend two things:
1. While shopping around reach out to local banks / credit unions in the area that you're investing in.
2. Be ready to provide documentation as requested to the lender. It's been my experience that the more seamless you make this process for the (i.e. fast response time, provide what's needed when asked) they tend to appreciate that and remember you as an easy client to work with. You can then Build that relationship with them for future deals!