How is your shoulder doing by the way?
Many with long term "tendonitis" don't have pure inflammation ("-itis" connotes active inflammation) but some amount of "tendonosis" a well (-"osis is short for "fibrosis", which is the replacement by fibrous "scar tissue" of the healthy tissue that was abnormally present.)
Tendons are meant to glide easily past one another, and past adjacent bone and ligaments.
With "tendonosis", the fibrotic, scarred tendon areas don't slide smoothly, leading to more inflammation - "tendonitis".
At any one time there can be more or less active inflammation - "tendonitis".
Over time, remodelling of fibrotic "scarred" tissue can occur so that the tendon glides more smoothly.
[Only occasionally does the tendon get so diffusely fibrotic or "scarred", that it will never glide smoothly, or so "stuck" to adjacent tendon, ligament or bone, that it will not respond to any other treatment but surgical removal.]
The best way to preventing "tendonosis" from occurring is to stop play during episodes of "tendonitis", to let the tendon rest and heal.
Realize that after periods of tendonitis, that just because the pain is gone, the remodelling of the tissue at the microscopic level is nowhere near complete.
That remodeling of tissue at the microscopic level goes on for months.
Too many who play sports don't realize they have microsopic tears in their tissues all the time.
The body is busy repairing those injuries all the time.
Those who play at a rate where the microscopic tears accumulate faster than the body has time to repair them develop clinical pain.
Those who return to heavy play too soon after the pain goes away, but before the tissue fully heals, likely will end up with some element of chronic fibrosis [tendenosis].
(Fibrotic tendons are not as supple and strong as "normal" tendons - in the below figure an estimation of 20% loss of strength in the tendon is given, but the exact percentage can vary widely, depending on how much of the tendon is replaced by fibrotic tissue.)