MAKE IT DIFFICULT FOR YOUR OPPONENT TO REMOVE BALLS THAT FAVOR YOU

Smart players do this for two very big reasons. For one thing, it allows them to build on their favorable position, so when they finally do get a shot, they can run more balls. And of course the other big thing is, if they can really lock up the cue ball at the same time they leave balls near their pocket, they might trap their opponent into giving up an immediate shot! The most basic tactic for making it difficult for your opponent to move balls that favor you is to leave the cue ball behind either the stack, or behind other blocking balls, so they cannot easily get to them to remove them.
Again, while you are trying to do it to your opponent, they are trying to do it to you, and so goes the dynamic of One Pocket.