I agree, stretching is parmount. I had a bad experience about two years ago with both elbows. I spent way too many $$$$ for occupational therapy getting back to normal. One of the things I learned is to stretch from my fingers to my neck. Today I play guitar about 5 to six days a week and limit it to 60 to 90 minutes. Sometimes I can get away with two hours. I stretch before gently and then stretch when I get tight sometimes while playing. As mentioned earlier in this tread, stretching is important and more important is to know how so you do not do more harm to already sore body parts. To get an idea of some of the stretches you could search YouTube and the Internet for "tennis elbow stretches" and "guitar stretches". This should help demystify stretching somewhat. Good luck.