Even when you're not in a race, avoid making illegal turns when you swim, so you don't get into the habit. Just like maintaining a neutral head position, doing what you're going to do on race day in practice will allow you to swim faster. A lot of swimmers think of the walls as a comfy little resting place, even if they're only "resting" there for a fraction of a second. However, if you want to swim faster, then this absolutely cannot be you. Approach the wall quickly, with your head down for at least two strokes in all of the strokes you're swimming except the breaststroke. This will help you get the lead you may need to beat your best race time—and the swimmers in the other lanes. When you're pushing off the wall, make sure to use a strong kick off it to keep up the speed you've gained. For a breaststroke, doing a full pull out can give you that extra edge. Continue to maintain a tight streamline while you're doing this, and you'll see that you'll soon be swimming faster than ever. If you're already using a powerful kick, you can go even faster by dolphin kicking off the wall. Dolphin kicking off the wall can make you go even faster, and having a strong underwater kick can increase your lung capacity. You may want to talk with a coach about this, because some swimmers go faster with long underwater kicks, and some don't, but some good general advice is to stop dolphin kicking and surface once you physically feel yourself slowing down, or if you reach the 15 meter (49.2 ft) or yard marker.

TL;DR in Vietnamese:
Tránh rẽ sai luật. Chạm tường nhanh chóng. Hãy vượt qua giới hạn bản thân. Đạp chân cá heo dưới nước.