2 on sheppard air for any written test. I've used them 4 times, only missed one question on 4 tests. Worth the cost. Outside of that, FAA has some decent materials, though navigating around them can be a pretty big shift from the military. Info is generally similar, just arranged differently. A good CFI is worth their weight in gold. And just like any checkride, ask around for gouge on examiners, as most have a script or common questions they go through. Advisory circulars are kind of like FCIFs or FCBs, lots of info out there arranged by topic, released or updated as needed, if you want to self study on topics. AIM is another good general reference https://www.faa.gov/air_traffic/publications/atpubs/aim_html/index.html CFRs are your regulatory guidance, part 61 and part 91 are good places to start. https://www.ecfr.gov/cgi-bin/text-idx?SID=2cae74ca26976e27b503c11b598ffada&mc=true&tpl=/ecfrbrowse/Title14/14cfrv2_02.tpl#0 If you're a military IP, don't forget to also grab your CFI. Just takes a written exam (again, use sheppard air to prep). Though once you get it, make sure you don't let your CFI cert go non current, since you'll have to do a checkride to reinstate your CFI. Typically all you have to do is a set of CBTs (multiple vendors out there, $100-200 for the course) once every two years.