[snazz]

With math specifically I had a good teacher in high school who made us practice in class together. He'd get everyone to sit around a table and he'd give handheld whiteboards to every fourth or fifth person (depending on the number of basic steps in the problem), and then the person with the whiteboard would do the first step and pass it to the person on their right. That experience stuck with me because just forcing me to get started (with help available) was enough to quickly clear up anything I was avoiding getting started on at home.

I still avoid doing things because they're emotionally uncomfortable occasionally, so I haven't really found a general solution. But it's gotten better over time and it's less of an issue when I'm more invested in something.