Hey guys, I've did a bunch of guest posting, very successfully. My main tip is to write a GOOD article, related to your website's niche. It must be a relevant article, written nicely (of course without typos), with some images included etc.Really, you must write it like for yourself! Add few links to high quality websites such as Wikipedia (or other in your niche) and a link to yours. My advice is to put links in anchor words, as natural as possible.
When you're set, find a bunch of websites that are in that niche, with lower and higher DA and start outreaching! Google a bit what is the best way to write an outreach e-mail and just be patient. It will pay off for sure! Good luck!