stihl #1

You will get as many answers to this as there are people to give them. My thoughts are:
Use synthetic oil and 89 octane fresh fuel, use a name brand bar oil, not cheap stuff from the bait and tackle store. I always add stabilizer also, but I have a lot of saws that may sit for a time so if you use the saw regularly then it may not be needed. I use a vacuum to pull fuel out of the tank when done and then start the saw and let it idle till it dies to get most of the fuel out of the system. Don't rev it up to use up the fuel since that will run it lean right before it dies.
Set the chain tension so that it snaps back to the bar when you check it at the bottom in the middle. Not too tight. Remember to hold up on the end of the bar while doing this, then tighten the bar nuts. A new chain will loosen quickly at first. Stihl chain is prestretched so not as bad as some other brands. Check the tension often, and loosen it up when you are done sawing.
Verify that the saw is not revving beyond WOT spec with the bar and chain on it. Doesn't hurt to set it 200 to 300 revs rich (slower) when it is new. Always warm up the engine before tuning or cutting. I start the engine get it off fast idle real quick, then slowly rev it up to about half throttle a dozen times or so, then tach it at WOT. By then you should be able to see oil being slung off the end of the bar when you hold it against the end of a log or a piece of cardboard.
A quality brand of saw will run better after a few tanks as it breaks in and may need tuning along the way.
Never tach a saw to WOT while cold. A big bore engine may cold seize.
HTH
Eddie