Gun Maintenance and Upgrading

Well i've had my gun for almost a month now and i feel like im gonna want to keep it for a long time. I kno mamy people go out and buy a new gun every week and thats their way of doing it. But im more of a sentimental guy which meams i dont like to make big changes unless i have to and would prefer to just upgrade what i already have. So my two questions are, 1: how do i care for and maintain my gun so that it lasts for a while? Some people i've asked say just to "shoot it til something dies and then upgrade the part that dies" but that doesnt seem right, u dont drive a car til it dies and then buy new doors because theyre dirty. This counts for internals and externals, ive heard some people talk about spring tension so any suggestions on that.
2: Upgrading, of course everybody likes to set their gun different from everyone else, so that it shoots harder, faster, has a better trigger response, etc etc. My problem is, how exactly do i do that? What parts do what? What should i go to first? Externally i can kinda figure it out, internally is where im stumped. Should i pay for someone to do it for me and ask to watch before i do it myself? And is there any place besides milsig and this sites own techs that can do it? Any suggestions there?

Sorry for the long post, i kinda had a lot to say...