The most important thing is to explain why the decision was wrong - that means saying which descriptors you meet and why. Use Advicenow's free Work Capability Assessment mandatory reconsideration tool  to help you write a letter that sets out your case to increase your chances. Be aware that not all ESA claimants need to ask for a mandatory reconsideration before they appeal. If you can go straight to appeal, do. The tool will tell you if you do not need to do a mandatory reconsideration.