Warcraft logs has a really awesome feature to compare yourself to people of similar ilevel, on the same fight of the same length.
After you click on compare, you will see the following options at the bottom of the webpage:
Select your name where it says “Select Player” and you can adjust the other options, but they’re pretty decent by default.
Use this tool to your advantage. Not only can you see how much damage you did compared to others of similar gear on the same fight, you can also compare the number of spells used, what spells account for what percentage of damage done, etc.