Each mental model is a skill. Like any other skill with practice you will be better and without practice it will decline slowly.
“The way to get that competency is to adopt the necessary elements and practice using it over a considerable period of time on a considerable area of complexity.” - Charlie Munger
Best way to approach practicing mental models is the same way on we approach going to the gym. You should be hitting the mental gym at least 3-4 times per week. You should have a workout schedule for each type of exercise you do. And you should rest between gym sessions.
The best method I’ve found is keeping to a strict daily 15-30 minute practice.
I use evernote as my gym. You can use a notebook, a note application or even a blog. I have a diffeerent sheet in evernote for each mental model.