Lots of good advice in this thread. Here are my top 5:
1. Keep track of posts when cleaning your keg. I find the best way to not mix them up is to only clean one at a time and then put it back on the keg before removing the other.
2. Keg lube. Every O-Ring, every time. Also, on the underside lip of the keg, as well as the inside lip of the lid. When in doubt, use more. A tube is cheap and it will last you forever.
3. After you rack your beer into the keg and close the lid, hit it with 30 psi for a few seconds to get a good seal on the lid.
4. Once you set the lid, check for leaks with a spray bottle with star san. Check it again.
5. Use an eva-dry portable dehumidifier inside your kegerator, keeps everything nice and dry.
5a. Build a DIY beer line cleaner (see link below). I absolutely love mine, when I finish a keg I flush the line with hot water, then flush it with some star san and I'm good to go. No wasted C02, no need to fill a spare keg with sanitizer or have a dedicated keg of sanitizer lying around like some of my friends do.
5b. 10' lines. I have had these from the start and I have never had an issue with foaming. If your current system came with 5', I would strongly consider replacing them with 10'.
https://www.homebrewtalk.com/f51/diy-beer-line-cleaner-226497/
Most of all, have fun while kegging! I definitely got frustrated a few times when I was first learning to keg, but now I look back at how silly I was being. Also, these are great instructional videos on the entire process (there are 4 total).
Cheers!