Practice what you don’t know first and most.
Seems obvious, doesn’t it? It is all too easy to start our practice with what is most familiar and comfortable. But that does not help us conquer what is difficult and uncomfortable. Especially when we have limited practice time and are overwhelmed by what we feel we need to accomplish. The simplest and most efficient approach is to start with what we are most unfamiliar with. After all, why practice what we already know when there is so much we want to learn and improve?
I learned this firsthand when there was a period of time where I had a lot of unfamiliar music to learn and limited time in which to learn it. I tried to make the most of what little time I had, ten minutes here, maybe a half hour there, if I was lucky. Subsequently I was amazed that by concentrating my full attention (and please note that I am emphasizing attention and not pressure) on the passages that I was least comfortable with, I made quick progress toward being performance-ready.
I credit my teacher during this time, Alex Murray, for this approach. He gave me many practical, common sense ideas to use in my practice, and this is one of what should have been one of the most ridiculously obvious of ideas.
So if you have little time to practice, start with the passages that give you the most trouble. Give them that laser-like focus that you have when your time is limited. You might be amazed by what you can achieve.