Are there any good ways to prevent onset of tendinitis?

Prevent tendonitis: If recurrant tendonitis, you may not be letting is heal sufficiently. Need 2-3 weeks of protection/therapy, then add a couple weeks for late healing. Recurrant tendon strain such as foot or knee strain occurs from abnormal anatomy: fallen arches or malalignment of knees, etc. Otherwise be sure to warm up sufficiently before exercise and don't inflict xs stress (heavy weight lifting). Easy does it!

Stretch and ice: Prevention takes planning. Taking antiinflammatory meds may help prior to activity, ice afterwards (even if not painful or swollen), hydration or recovery fuel, massage, stretching, etc. Hope this helps.