Very short faster sets like 10x25 as opposed to doing longer drawn out swims. Then as you pick the cadence up on those it will start to translate into a faster cadence in the longer swims.
But a faster cadence is not always the best way to go. Fast cadence is great for swimmers with less upper body strength and/or shorter arms. A lower cadence seems to work best for people with more upper body strength and/or longer arms.