Best tip no one ever mentions is to use a pair of vise grips, split joint, channel locks or similar pliers to push roll pins in. wrapping the pliers in a rag and clamping down almost guarantees a scratch free job and eliminates the need to tape the receiver up.
ETA: Also if you're building a polymer lower make sure all the holes are in spec before you start shoving detent springs and detents in them. I was installing the front take down pin on an FMK that was out of spec. I put the spring in and then the detent, I pushed it down with a razor blade and slid the take down pin in place. Well, the detent never popped back up into place. The hole was too small and i had wedge it in there thinking I was fighting the spring. There's no way to hammer it out from the other side on that hole. I tried several things to get it unstuck including heating it, drilling it, blowing compressed air in the vent hole and finally slamming it on the ground repeatedly maybe giving it a few kicks here and there and it never budged.I set it on the shelf and decided I would just have to hammer the detent in further and use KNS pins, maybe just turn it into a .22 build. Well I was looking at it a few weeks after the incident, thinking about how I would never buy another shitty ATI product again, and notice that after all that time the little spring had pushed the detent out. I re-drilled both detent holes with a 3/32 drill as well as the take down pin holes, which were also out of spec, and now it works fine.
This post was edited on 3/18 at 8:45 pm