When I was young I was always pushing to improve. Never stopped to enjoy what I had already accomplished with my playing. The criticism was one thing that caused me to quit. It helps me to practice something that works on skills I am trying to learn then spend some time playing music purely for enjoyment or fun. Find pieces that I like to play, not just restricted to the instruction book series. For me that has been Christian music on the piano and maybe Christian and fiddle music on the violin until I can get back to playing well enough that I can enjoy my playing classical pieces. Work on skills but don’t obsess with perfection on music I don’t enjoy. When I get tired of even pieces I like, go on to something else and come back to it later. When practice deteriorates and it seems I am playing worse, take a break! Sometimes rest makes a huge difference and the next time I play I can progress. Be more patient with myself! Celebrate what I have accomplished instead of getting discouraged.