Some tips from limited experience, in no particular order...
Start with a quality LPK from a reputable dealer. I like Brownells branded LPKs.
ALG QMS triggers are great, the ACT is even awesomer.
Get a milspec buffer tube.
I use a razor blade to hold the detent and spring down when installing the front take down pin. I taped a dull utility razor blade so I could hold it safely. I use the bare portion of the blade to hold the spring and detent down while inserting the take down pin. A helper really ... helps with this.
Have spare detents and springs. ...
Make sure the ear is supported on the bottom when installing your trigger guard, many have snapped these off and ruined their lowers. Place the lower on it's side on a scrap piece of wood. When you are pushing in the rear pin, it can snap off the lower ear if not supported.
Use a channel locks or pliers to press in the bolt hold open latch pin. Also, you can use some tape to prevent scuffing the finish.
Don't crimp the rear take down pin detent spring...have spares.
Verify the orientation of the fire control springs....they can be installed incorrectly (shame face)
Some grips may require a washer or two on the grip screw...(Magpul OEMs). I like to chase the threads first to ensure the screw goes as far as it needs.
Don't crimp the safety detent spring when attaching the grip....have spares.
Carful with the buffer retention spring and detent when installing the buffer tube....have spares.
Stake your castle nut ONLY when you are sure you the end plate you want....
Function check to ensure you got it right.
Add some lube and dry fire the lower a bunch to smooth everything up, but DO NOT let the hammer slam into the lower. Use your support hand thumb to catch and reset the hammer...You can do this about 100 times during a tv commercial.
If your fire control pins back out, your springs are probably in worng. (shame face).
Assembling front take down pin is not hard but if you slip your pin will fly away..RNGR1
I use somthing like this..
Watch this before try to assemble front take down pin..