Learn chess openings
Each opening is a path of variations, and each variation is learned, played and then quizzed. Pick the side you want to fix first.
If you are starting out, you need fewer openings than you think: one for White, and an answer to 1.e4 and 1.d4 as Black. Three, not thirty. The courses below are whole repertoires, so picking one settles that side of the board for you.