1. Give yourself permission to just try, for a little while
2. use fear-setting for really tough moments
A technique that I've found helpful when dealing with anxious thoughts is I become mindful of the anxious feeling, realize what I'm feeling anxious about, and then give myself permission to just try, regardless of the outcome. I'll explicitly granting myself permission to "just try" and even throw in "just for a little while, see how things go". This at times has turned into a productive, multi-hour session.
Tim Ferriss talks about a technique use to confront fears, called "fear setting" [1]. Essentially, I put together a 3-column table and think through the worst that can possibly happen. It helps me think about risks and realize what I can handle. This helps to manage worry.