purchasing a physical template to mark your arcs more accurately.
I've done a little trial and error on this already so that you don't have to.
It's a good question and there are a bunch of reasons why we hit hobby slumps. A "slump" can mean anything from becoming bored with what you're working on, bored with hobbying in general or unable to get painting again due to other things getting in your way. After some revelations of my own, I'm going to finally try and offer some suggestions and tell you what works for me.
Also, worth noting... I may use the word "painting" a lot, but really, that's a term I use as a general reference to the hobby. I could be talking about sculpting green stuff, cleaning mould lines, building terrain and so on.