follow the instructions to the t. If you have a hard time doing it yourself get a trusted friend or family member to help. You can do a lot of it on-line and by mail. That might be easier for you and less stressful. From what I understand from talking to people that work for SSA is that most denials are because something is not filled out correctly by either the applicant or medical people. SSA employees should treat you with respect and be helpful. If by chance you come across one that doesn't, get their name, write it down and then ask to speak to a supervisor. Work you way up the chain if you have to. If you should happen to get denied, keep all paper work and appeal.
BTW SSA employees can and do get fired for treating applicants badly. They should always be reported if they fail to do their jobs. Most bad press comes from those that never applied or didn't follow through. Remember, you paid into it (or not in the case of SSI which is based on need and income) and they are they to help you.
Edited- Forgot to paste in the website.
http://www.ssa.gov/disability/