Some hard-to-spot but occasionally useful rules, for when you've mastered all the others.

Three Trapped 1's

The 1's never appear as all "actual" 1's; at least one is an "effective" 1. The mine is always behind the middle 1, and the other two are safe:

Four Trapped 1's

Like the Three Trapped 1's, at least one of the 1's is an "effective" 1. The first and fourth squares will be mines, and the other two safe: