upgrades everyone needs

So i thought i would start this category with some tips and advice that i really think everyone should do.
first off,
Everyone needs to swap the connector on their AEg with deans connectors, the old large and small tamia connectors far too out of date.

everyone needs to swap the stock hop up spacers, for the concave spaver

If you havent already, you need to upgrade to a 9.6 battery, if not higher or a lipo.
its not a must, but you should upgrade to a tight bore inner barrel.

I cant agree more with you about the Deans connectors it makes everything that much easier.

I 3rd the Deans.
If your going to run a "concave" hop-up nub, you need to shave the "hump" out of your hop-up bucking to take full advantage of the concave nub.
I wouldnt run anything smaller than 9.6v. 10.8v works very well and you can fit one in most AEG's or at the vary least, get a PEQ box.
Before you run an 11.1v LiPO, you should shim and AOE your gearbox. A 7.4v LiPO is more forgiving but you might as well run a 9.6v.
If you plan on running an 11.1v LiPO on stock internals. Stay under 20c discharge.
6.03, 6.04 and 6.05 are a all considered tight bore barrels. Anything smaller than 6.03's performance increase is debatable. A 6.05 high quality Bull barrel will usually perform better than a cheap 6.01.
The biggest accuracy improvements will be seen with .25g, .30g BB's (for 350-415FPS) a good hop-up bucking/nub. A tight bore will increase the accuracy as well but not as much as the BB's/hop-up improvemants.

with what autoxgt said, you can spend 1000$ on all the best accuracy parts to make your gun as accurate as possible, but it wont matter if your not using the right bb's.