Find a good stripped lower, PSA and CMMG are the brands I use and others will suggest some good ones as well. Pick up a LPK from the manufacturer of your choice and get to work.
As for the trigger, there are a lot of good aftermarket ones available. I have an 18" SPR-esque build that has the Giessele SDM trigger and I love it. It's a bit pricey, but definitely worth it.
Good equipment will never be a substitute for good training.