I know it's not for everyone but the first thing I do after getting a new gun and after staring at it for a few days in rapture... is to send it to my favorite gun doc.
He takes it apart, cleans the gearbox, make sure everything works well together (downgrades the spring if needed) reshim/relubes the gearbox. Replaces the crappy plastic parts and wiring manufacturers insist on installing to save cost and ruin their reputation and installs dean connectors. He installs any new parts I have for it (UBR stock, front kits whatever) and makes the upgrades I need all at the same time.
It's not for every budget but on the other hand, I don't have 6 crappy guns that cost a fortune in maintenance and never work properly. I have two excellent guns that shoot far and straight, 1 excellent pistol, 1 nice WW2 Thompson that will go through the process soon, just got the wood kit and the metal lower for it. Name another serious sport that don't take their equipment to a professionnal!
Don't buy cheap and dont skimp on good upgrades that work well together. The worst thing you can do in any project (not just airsoft) is to buy a cheap piece of 废话 and try to make it work as well as a quality item by adding a ton of parts that are not made to work together as a whole.
Regarding maintenance, 100% oil free silicon on a rag through the barrel twice in the summer. Dont leave any oil in the barrel and don't go all the way you might break the rubber hopup. Send the gun to your Gundoc during the winter season to repair/replace any item that is broken or on the point of breaking. A squirt of silicon oil in your mags twice in the summer or after playing in the rain. Dont over do it, it will trap dirt and create more problems then good.
Sorry for rambling