Is the task too vague? If so, making it more concrete helps. "Do taxes" is impossibly vague and scary and the brain rebels. "Make a list of all expenses this year" is better but still large. This is the most common actually helpful advice I've found. But also
Do you not actually care about the task? Having a grand overarching goal for your career/life can help you make sure the task is worth doing. Or for something like taxes, you can say "this helps me achieve my goal because if I don't pay my taxes I'll probably go to jail."
Do you not believe your project will succeed? This is a subtle one I only recently discovered. If I'm working on an app or a business idea and I get to the point where I don't believe it has a chance, I strongly lose motivation. Some say this is a survival mechanism - if a hunter gatherer had a plan to kill a wooley mammoth with a spear up close and that'd probably result in death, a strong sense of "procrastination" could be a lifesaver.
Is it resistance to something that threatens your identity? This is a fun one - maybe you've internalized that you don't finish projects (I've had some of this I think). Finishing a project would threaten your "identity" of a non finisher, and some part of the brain _hates_ things that threaten it's identity. I think this one you just have to figure out a way to push through, and give that part of the brain fodder to convince itself that it's identity is not of "doesn't finish projects". The same can be true of earning money, and other kinds of success.