Prepare the next small step while your interest is still easy to reach.

Enthusiasm is a resource with a short shelf life, and the moment it fades is exactly when setup work feels impossible. Right now, while the thing is still interesting, you can open the file, buy the part, write the first line, book the room. Later that same task will require willpower you may not have. What you are really doing is leaving a note for a less motivated version of yourself.

At the end of your next good working stretch, spend five minutes preparing the beginning of the following one. Leave it half open rather than tidily closed. Coming back is easier when the first move is already made.