The reason you're getting downvoted is there isn't really any "efficient" way and this question gets asked every other hour. Find a level of problems that is fairly difficult for you (200-300 difficulty over what you can solve in contest) and keep solving problems, you'll come across new ideas and your overall solving skill will improve.

Also don't immediately look at the editorial if you cant think of how to solve it right away, as long as you have some idea that you think could work, try it. If you have absolutely no idea after some time (say 30 mins or so), then look at the editorial. (Others may suggest different methods, the core part is try to think for a while before seeing the editorial)