Push yourself past your comfort zone.
At some point, you will say to yourself, "I've never done this before" or "I don't know what I'm doing." When you have that feeling of giving up:
You've decided to start, great; keep pushing forward. If you're thinking of a way out where you can quit and save face. Don't do it. Don't give yourself an out. Just don't. Don't give yourself any options. Either you succeed or fail, and if you fail, dust yourself off, get your mind right and try again.
You must get comfortable with being uncomfortable because fear kills more dreams than failure ever will.