I have written an article about fixing the wrist injury
I got this year. It includes a lot more about specific practical stuff I have found to keep tennis specific injuries away and build my game.
In general I find PRICE
works for me for pulls and strains. The p and r are most important long term. Protection is about still playing but avoiding hurting what's injured. For each injury I explore what that means. Generally it means improving my technique and learning a new way to get the job done. Frustrating at first but always beneficial long term.
For minor things I often find protection is all thats needed. That can be a brace or support or it can just be adjusting your technique to take the load off the affected area. I protected my wrist by not doing a full serve so I didn't extend the wrist as much and I avoided certain shots. For a groin strain I found not running as far for balls and using a shorter stride was enough to not aggravate it and let it heal. For both I improved flexiblity and strength once the pain had gone.
When the pain goes you will start the next phase of rehab. Strengthening and flexibility. I don't generally get the same injury again because I fix my technique so it won't cause it and because I make myself stronger and more flexible. That's what an excellent sport physio taught me and it works like a charm.
Each injury has its specific fix so it's up to you to find which specific things it needs but price is a general approach that works well to get it healing however it will leave the related area weak and tight so strength and flexibility along with working slowly back to a full motion will bring the full fitness back. Until you have full strength and flexibility and coordination back you will probably get the injury again. That's why I kept getting ankle sprains. I didn't do the rehab work properly. Once I did I was fine.