@dottyp
I have found that the secret with comparison (in all aspects of life) is to learn to view it--not as who is better/worse, but "What can I emulate?" You can learn from anyone or any situation with the right attitude. Try to have an outlook of unity rather than enmity. There doesn't have to be a conflict between your art and theirs. If you stop looking at it as, "They're so much better than me." and start looking at it as, "What are they doing that I can learn from and incorporate into my work?" it should help keep a positive spin on the excercise.
When you find yourself going in a negative direction in your thoughts, remember that you have the power to choose which thoughts you entertain and choose to believe. Tell yourself that the first step in becoming better is to identify the things you can improve. It can be tough to change the pattern of your thoughts, but with practice, it is possible.
Something to keep in mind is--just trying to suppress a thought can sometimes end up magnifying it. It's good to acknowledge and challenge the thought instead. A friend who struggled with self-doubt shared a method she was taught that helped her. When she had a negative thought, she replies in her mind, "Thank you for sharing. I choose to think otherwise." It might seem a little silly, but it's an effective way to address and dismiss it. For some people, it helps to write down the negative thoughts/feelings, then destroy the paper (crumple, tear/shred, burn), or cross it out and write something uplifting.
If it's too overwhelming, remember not to overload yourself. You might want to examine it just long enough to pick one thing to work on. Then write a note on your calendar to come back and look for one more thing.
Making a plan of action also helps me see things in a good perspective. Write down one thing you want to focus on first, and what specific steps you will take to work on it, plus when you plan to work on it. Having a plan is empowering.