I try to keep track of which front gear I'm in, so I don't accidentally go into the extreme crossover (biggest front with biggest rear, or smallest front with smallest rear). At night that gets tricky. I have a twist shifter and the numbers are worn off so in the dark I can't tell at all. So what I do if I forget which front chainring I'm using, is try to shift down without pedalling, and then shift back. If I was in the smallest, then I can't shift down at all.