Below is a link to Josh Andrew's book which is an excellent starting resource, and an e-book from Dave Van Horn about NPL investing. https://www.amazon.com/Paper-Profits-Beginners-essentials-mortgage-ebook/dp/B06Y4C7X6Y/https://www.pprnoteco.com/wp-content/uploads/2016/08/Intro_to_Note_Investing.pdf

My first did well based on selecting an area that we frequent.

@Brienne Metcalf first off @Kevin Sobilo's points are all excellent. 

While advanced features are available for purchase, partners receive 1,000 free skip traces each month to support their efforts.Utilizing ResourcesBiggerPockets is an excellent resource, and we support its use.

Small business with excellent service and better yet great photos.

After this tenant leaves, you must clean/repair, market, screen applicants, select an applicant, collect the deposit and rent, get them moved in, etc.

Cost segregation is excellent for STRs because you can take it to offset the terrific gains on this type of property as well as off-setting it against W2 income if you are materially participating in its management. 

Each approach brings its own strengths, and the BRRR strategy is excellent for building long-term wealth.

There are only a select few areas to steer clear from, but even those are getting better.

Very selective process, and geographical regions- but this is an AMAZING tool for some people.