Replace all the fuel lines, especially inside the tanks at least once a year or every 6 months if you store the tank empty and use 30% nitro, the lines will rot.
Replace the rubber dampers in the head once a year or when they start to show some signs of getting soft (nodding of the heli when maneuvering).
I clean off the mainshaft and tailshaft at the end of a flying day or at the beginning and relube with tri-flow.
Personally, I run the engine dry at the end of the day, pull the fuel line off, add glow heat and run the starter for 5-10 seconds after the last kick. Then make sure to shut the carb off, I'm now getting in the habit of manually moving the servo to full stop after turning the radio off. Idea is to keep any air from moving in and out of the engine which will get moisture in there and rust out the inside of the engine. putting a stopper in the exhaust also helps to keeps it from breathing and keeps the oil from dripping all over.
keep an eye on your battery pack. Replace it if it doesn't charge up like it used to. Probably every 2 years is a good idea, every year if you don't keep track of them when storing. I'll push my packs longer but I'm watching them.
If the engine was running great and starts to become hard to start or won't hold an idle your glow plug may need to be replaced.