I use several techniqes for beach swim starts, depending on the conditions and the situation.
If it’s calm, then just swim.
If the waves are under say 2’ tall, I generally just swim through them.
If they are over 2’ tall, I generally dive under them, with a sorta “kip” action as I grab a pull of my stroke.
If they are crashing, then I generally dive under them too, but add a couple of dolphin kicks to stay under a little longer.
Remember, you want to pop up between waves, for a breath. And remember to relax when you are under water. Depending on water conditions, it can be cool to look around and check out your fellow racers. Oh yeah, when you pop up out of the water, take a stroke and breath, (to the side) then look forward for the next wave and decide your strategy for that one. Swim hard between waves, then rest for your last stroke to get ready for your dive uner the wave.
If the bottom is close enough, you can grab it an use it to launch yourself forward, or if the waves are really big, just to grab and hold on while it passes!
I LOVE big wave swimming. I know most others don’t like it, so that makes me even better in big wave races.
I have an open water race coming up in about 5 weeks. One year I swam it, it was an outgoing tide (from the harbour, around a headland) with an incoming wind! The waves were not that big, but they were really steep! Swimming into the waves, you’d lift up, then pop out of the top of the wave and then drop what would feel like a mile, and splash on the water below. I LOVED it. I heard several others took on too much sea water and were puking their guts up! Hilarious I thought.