I used to start projects, get overwhelmed then give up and start a new one (mostly home renovation stuff).
Since diagnosis I've learned to break things right down as you suggest and fully complete each task before moving on.
For example I'm decorating my dining room and won't move onto the next wall until the previous one is finished. In fact one wall has a couple of alcoves which are a bit fiddly, so for that one I've broken it down even smaller to finish one alcove before moving onto the next.
I'm half way through one of them (no progress/motivation since Christmas) and currently more interested in garden related things, but in the mean time the room is still functional with just one iffy looking bit instead of it looking like a building site!
I used to beat myself up for not being able to finish things, so it's nice to finally be able to relax and ride those waves!