I use shell 91 octane ethanol free gas for the mix
Ethanol free gas is a must. If you can't find ethanol free gas in your area, then spend the extra and buy pre-mix.
I have an FS55RC. It just celebrated it's 10th anniversary by having to have the carburetor replaced. When I picked it up from the shop I asked if there was anything I can do to prevent this from happening again. The tech told me to use only ethanol free gas. I have since received the same advice from a number of sources.
Last weekend I used the trimmer for the first time after getting it back from the shop. Per the instructions I had been given, I used 50:1 mix made with ethanol free gas. The trimmer ran great. It had more power than it has had in a very long time. The engine ran even.
I made the same fuel switch in the leaf blower. It also ran better than it has for some time. All my small engine tools are now getting only ethanol free gas.
except for fuel, the only other annual maintenance I have done is greasing the head, as has already been recommended. That and adjust the carburetor settings every couple years. The first spark plug lasted 9 years before I had to replace it. These are great machines. Hope you enjoy yours as much as I have mine.