First, respect that the ocean is stronger than you are. The force of even an average swell is far greater than anyone can resist. That's why it carries you along. But when those get to a certain point, they'll carry you down. Don't go surfing when the conditions are greater than you can handle. Don't push the limits until you're very experienced.
Next, be aware of the ever changing patterns in the water. Riptides can appear seemingly out of nowhere. Sometimes they're just an inconvenience, dragging you down the beach away from the spot on shore you want to reach. But, those surface currents can also drag you out to sea, especially if you're fatigued. Stay strong and get out of a rip current as soon as you sense it.
They're not difficult to spot if you're alert. They appear as calm flows, usually as a strip or channel within surrounding turbulent water. The color will often appear slightly different. They don't drag you under, but they can put you far enough out that you can't return to shore. Then you tire before reaching safety and go under. Swim or paddle parallel to the shore until you're out of it, then return to shore if you're tired.
Undertow is similar, but in this case the water flow is under the surface. When you're on your board that's not usually a problem. But if you fall, you'll often go far enough to reach it, and it can drag you down further and away from the shore. Again, try to swim parallel, at the same time rising to reach the surface. Swimming directly up makes it harder to reach the surface.
One of the more likely problems that can lead to drowning while surfing is being hit with your board.
Even the most advanced surfers fall of their surfboards at some time. It's difficult, but necessary, to be alert when you're on the way into the water. Try to note which way your board is moving. When you return to the surface, don't assume your board has floated away. The board is almost as likely to move back toward you as away from you. That's convenient, but dangerous.
If you use an ankle leash your surfboard can't move far away. That means you can be the cause of it hitting you if you don't move the right way. Practice in a swimming pool to get used to manipulating your leg and the board to grab the board before it hits you in the head. Being knocked unconscious by a surfboard is easy and, as you're often reminded, you can drown in a foot of water.
Develop into a strong swimmer, watch the ocean and stay alert. Your odds of drowning will be very low.
Also, make sure you have the right sun protection swimwear gear, to be protected again the sun UV radiation and its damaging effect on your skin.
