Bad swings, old tendons, frequent play are the top causes of TE. Only one of those things is easily remedied.
If you have those 3 things and use a stiff frame and stiff non-resilient string, you exacerbate the problem.
I've dialed in my elbow after struggling with TE and GE and know what gives my 55 year old tendons pain and what doesn't. Any poly stiffer than Cream is a no-no.
You hear 'technique' a lot when it comes to TE or forearm pain. Sometimes a stiff racquet set up will make bad technique apparent more readily.
The problem with bad technique is:
Over-extending on your backhand or slice(not following through and the elbow taking the brunt of the arm stopping). You want a smooth effort, and swing through. Don't force your arm to stop - let the natural motion end itself. Some folks may need to purposefully keep their arm bent a bit during the swing to prevent TE as well.
Extending/supinating on the serve - unavoidable for most, especially if you have a Sampras style serve - which my coach in HS broke me of very quickly by simply teaching me to turn more on my swing and come across my body(not that Sampras had a bad serve, quite the opposite, but it can easily cause forearm issues). Stretching and a brace help here.
Playing even after feeling pain. Pain is your body telling you to stop being stupid. Soreness is your body telling you that you are a weak little baby - know the difference. And don't push yourself when you are feeling very sore because you saw some muscle builder do it. What you didn't see was the guy reaching for steroids before and after the workout.
When your body tells you to stop - stop. Taking a mild NSAID like Aleve(Naproxen), or Ibuprofen to help heal faster and keep the inflammation down isn't a bad idea. And - Rest!
Stretch your arm during warm up. I see people out there stretching their legs and shoulders and trunk, but no arms or forearms. Extend your arm behind your back like you got to scratch in between your shoulders(both from the top and bottom) - genty stretch all those tendons out before you play. Place your arms outstretched in front of you, grab the back of your hand and pull the outside of it over to stretch it and your arm. Supinate that wrist and elbow gently, stretching the tendons.
Try not to just jump in to a game - always warm up gently.
Wear a brace until you are warmed up, or just wear it all the time like Kygrios. He's smarter than he looks. It also keeps your joints and tendons warm for blood flow and relaxes and supports them.
If it's cold out, take it easy until you are warmed up.
String lower, use springy strings, get a flexible racquet, stop hitting the frame on a 72RDC stick, and get in less fights. But, most importantly:
Stop diddling yourself so much! Every child is sacred and yer arm has a limited amount of lifetime diddling in it!