#string trimmer maintenance

I've been using my Husqvarna 128LD string trimmer for a while now and I just hit 50 hours on it. I'm pretty excited because it still runs like a charm. I've been doing some research on how to keep it running smoothly and I found out that I should be changing the air filter every 25 hours or so. Has anyone else out there had any experience with this model? What kind of maintenance schedule do you follow?? I've also been thinking about investing in a community garden and I want to make sure I've got the right equipment to keep everything looking nice. Maybe someone can give me some tips on how to keep my trimmer in good shape...