I've just started using OnX this year and love it. Most of my advise are things that have already been mentioned:
- tracker is a great feature; remember to start it at the beginning of each hike, then stop it when you get back to camp
- ability to toggle back & forth between topo, satellite imagery, & hybrid (both topo & sat) was a lifesaver on a recent Colorado elk hunt
- remember to download offline maps of your area before you head out; I like to get a low resolution map of the entire area, then higher resolution maps of each specific area I plan to hunt
- use phone in airplane mode to save battery; if you're backpacking, make sure to take extra battery packs to keep your phone charged
- I like to mark waypoints on my computer before I leave home (troughs, ponds, springs, possible spots for camp, trail cams, glassing, etc.); these should automatically sync to OnX on your phone and make finding these places much easier while you're out hunting
- if you're adding a lot of waypoints, it helps to use the different types and colors to keep them organized (like red for roads, blue for water, etc.)
Good luck! If you find any other useful features let us know.