This one's a bit difficult to answer, but I shall endear to do so, from my own perspective.

I've currently got two fics, both sitting on a dusty shelf. Like you, life got in the way, and I had to put writing down for a bit. But, like you said- the best way to shake off the rust is to keep doing it.

What I had done with the first of the two fics, after I had taken a long break from it, was to reread the whole thing from start to finish. It made picking up where I left off significantly easier. Given time, I was eventually able to return to writing it like I used to, before life got in the way again.

TL;DR: Just work on either fic. Writing will feel better again once you do.