First, you need the ABCs of police and law enforcement survival. Buy the Tactical Edge, Street Survival and Tactics for Criminal Patrol. It’s a 3 book series and this is probably the ground work for most typical police training today. They’ve been around a long time and have earned a great reputation.
Then buy Handgun Combatives by Dave Spaulding. Generally I don’t recommend books written by gun rag aficionados, but Mr. Spaulding really nails the nuts and bolts of gun selection, mindset, etc. in a small book. Or you could scour a lot of the classics by Col. Cooper and decide what is still applicable in today’s world. Personally, I’d save the time and buy Dave’s book.
Next, Masaad Ayoob is one of the foremost legal experts in deadly force encounters. I recommend his material if for no other reason than the “legal” aspect of use of force everyone packing a gun should know. I’ve never used his stuff for “tactics” per se, but he is one of the better respected in that regard as well.
Clint Smith of Thunder Ranch fame, I have mixed opinions on this guy. Everyone our department sent to TR came back with some pretty silly notions in tactics that I personally and professionally do not agree with. Could be our officers, could be what Clint taught, I have no idea. I found the material in the Tactical Edge to be much sounder.
Then there is TacPro. I’ve heard a lot of great things about this place, though I’ve never personally been there. I do agree with the shoot and scoot method of walking and firing that is taught there vs. the “crab walk” taught at other places. Which demonstrates to me that at least that particular tactic was well thought out.
Lastly FLETC is a great place to get training materials. They haven’t been shy with providing materials to my dept.
BTW…if you are not a sworn LEO, you will have difficulty getting your hands on some of this material, and rightfully so. If you are not a LEO, buy Dave Spaulding’s book and go to TR or Tac Pro and call it a day.