Way to get the best "deals".
0) Know exactly what you want.
1) Shop around to get a feel for "regular" prices.
2) Sign up for Email specials at all the major vendors of AR parts: Midway, Brownells, PSA, Bravo Company, Primary Arms, Joe Bob's Outfitters, Model 1 Sales, etc.
3) Wait for sales on what you want.
4) Buy it when you see a good price