Learning to surf, be it at a nearby beach or farther away, like at a surf resort in El Salvador, is an amazing experience. It's also a physically taxing one if you don't take care of yourself. You're running, swimming, and trying to control a board on a wave with your muscles and shifting weight; that's not exactly light work. When you first start surfing, you may find that you don't feel as strong as you normally do because of the unfamiliar motions. Giving yourself a little extra care will help.
Drink Fresh Water Regularly
It's standard to tell someone to stay hydrated, but when you try surfing for the first time, keep drinking fresh water on a regular schedule. You may get so wrapped up in trying to stand up on that board that you forget to drink water, and then before you know it, you have a dehydration headache and aren't concentrating well. Plus, the fresh water will combat the effects of any salt water you accidentally swallow if you fall off the board. Yes, you may have to go back and use the restroom more often, but that's a minor annoyance compared to how dehydration can make you feel.
Stay in Your Lane
When you take surf lessons, the school will have you practicing in a particular spot along the beach. Stay in that area. Chances are that's a particularly calm section of ocean, and away from that area, there may be reefs that make the waves harder to ride, thus increasing your risk of injury.
Outside that small zone, you'll also have to deal with more experienced surfers who may not take too kindly to extra crowding. The surfing instructors will teach you basic wave etiquette, but it's best to stay in the area in which you're learning. Don't wander off to practice away from the group unless the instructor gives you the OK.
Eat Something, but Not Too Much
You need to eat something before going out to surf, but you don't want to eat too much. For one thing, if you eat a lot, you could feel kind of tired when you try to surf. Plus, if you are prone to reflux, the face-down swimming/paddling part of surfing could aggravate your condition. Have a light snack or meal a couple of hours or so before going out to surf.
You won't regret learning to surf at all, but it will be a lot more fun if you're feeling well and not getting into tough situations. A little self-care will have you feeling in top shape.