the best way is using tactic trainer.
if you have a tactic trainer tactic. don't move anything until you have solved it(move 2,3,4 should be found within 1 second and come as no surprise ). think really hard. don't look at the solution.
treat tactic trainer as a chess position trainer. Try to think what you would play as if it was your turn in a online chess game.
you shouldn't care if it was a online game or tactic trainer.
you would look at the positions the same way.
Simply put, what's the best way to improve your tactical ability? I'm currently doing tactics trainer and intentionally playing tactically sharp openings to get better at tactics, but what do you think?