One transition I recommend would be the match cut.

It's not flashy; that's kind of the point. Done well, nobody registers that a cut even happened. No wipe, no dissolve. The cut does all the work on its own.

It's also one of the more approachable places to start. The simplest version is just lining up a shape or a position between your outgoing and incoming shot. From there it goes as deep as you want: matching the direction and speed of motion, matching color and light, all the way up to the kind of cut that makes people rewatch a scene just to catch how it was done.

Anyone else have a transition technique they think doesn't get talked about enough?