What do you want to tune and tweak specifically?
When I'm assembling a lower, I do a little prep on the LPK, I radius the detent tips and if I'm going to use the LPK trigger, I deburr the disconnector, hammer and trigger, then I do a "15 minute trigger job".
On a large frame AR (LR308 type in my case), the takedown pins are large enough to use an adjustable reamer to fit oversize pins for a no rattle upper to lower fit. It's not terribly important but nice.
On an upper, match guns will lap the barrel seat to square it with the bore and some people will bed the barrel extension to the upper with loktite.
Installing a barrel is pretty easy with an armorer's wrench. Some handguards make it difficult with odd barrel nuts. The torque is supposed to be 30-80 ft-lbs, I prefer good and tight. The issue becomes getting proper torque while aligning the barrel nut with the gas tube hole. On a standard style toothed barrel nut, I'll tighten it to good and tight and then Dremel off any tooth that blocks the gas tube. After the handguard goes on you'll never see it and it doesn't need every tooth.
Once you have your AR together, there is a bunch of stuff you can change for ergonomics.
If your rifle is over-gassed, you can try heavier buffers to slow it down or an adjustable gas block (usually more effective). If your rifle is under-gassed, you can enlarge the gas port, try a krink brake to add a bit of dwell or maybe go for a light buffer and carrier (I haven't seen that fix a problem).
A muzzle brake can reduce recoil at the cost of muzzle blast and noise.
Reloading can let you get the most out of your barrel.
Free float handguards are a key to accuracy.
If you need a better trigger than an LPK trigger with a 15 minute trigger job, there are lots of match and drop in triggers that work very well so there is no need to learn how to do more than a 15 minute trigger job.
Beyond that it's just being handy enough to get your parts to fit together. It can take some filing if you have minor parts incompatibility. It can take machining if you are trying to build a real oddball setup. Sometimes it takes buying new parts when you find a genuine this won't work with that incompatibility.