If the first step is too big or the end goal is too far, I cut the first step into smaller steps, and try to find a tempting intermediary goal.

Right now, I'm restoring an old motorcycle, and it's not going well. A bolt broke and I need to extract it from the engine I just reassembled.

My end goal now isn't to ride a shiny vintage bike, it's just to get it running. The first step isn't to extract the broken bolt, it's to open the engine again, a ten minute job.

Start small, set reasonable goals, and be careful about premature optimisation.

Start working on something small and easy that's related to the thing you're actually trying to accomplish, and that'll help swap the broader context into your head that you need to work on the larger problem.

Break the larger problem down into tiny little pieces that are easy to accomplish. Put them in a list. Pick off the easy items first each time you're trying to get started.