That depends on how good you are already. Beginners progress most by learning not to hang pieces. Up to the ~1000 elo level you will win by simply not blundering with little to no opening theory. After that the breadth of scope opens up a lot. I got to ~1750 over the board almost completely ignoring openings beyond move 4 or 5. Watching videos on strategy, how should I be arranging my pieces / where do they "belong", and simple tactics will take you far. Openings are important, I study them more now, but I wouldn't get bogged down by them. Picking up an intuition for analysing a position and it's thematic ideas is key.