This applies to all your petrol (Gas) powered machinery.  Always use fresh fuel and try and avoid fuel left over from last year.  It will save you a lot of running issues and better starting.

Two stroke fuel, always give it a shake before use to keep the oil mixed evenly in the can.

Hiya Mick, I tell everyone the same, I was working on a strimmer a friend brought me today and wouldn't run, first thing I did was check fuel and it was like jelly in the bottom of the tank, I cleaned that and cleaned the carb and it worked like it should.