Smooth swimming is ideal for a swimming pool, but is no good in choppy waters. A high elbow recovery, resembling the action of zipping a zipper with each stroke is required, or else, your stroke will be eaten up by the water. Hence, the arms have to go well above the water.
Keep on Rotating
Another crucial tip is to always begin swimming on your side, more so the upper body. It will lead to lowering the frontal area of resistance. That in turn will get the stronger muscles of the back involved, to get a stronger pull and increasing the length of your stroke.
Along with that, the movement of the legs is very important. One should ideally be swimming in a horizontal position in open waters. However, do not depend too much on your legs to help you move ahead.
On the (Peri)Meter
When there is a large number of triathlon participants, if you stick to the inside of the group or outside, you will be able to swim better and at a steady place. You will be spared of altering your pace to match the group by doing this, though drafting can get a bit difficult to achieve.
Tried and Tested
Another tip is to test and check out the water. See what the temperature of the water is before a race or even a training round. If you are talking about a race scenario, then the best bet would be to go in the water and do some warm ups.
In case it is neither, and you are going to swim just for fun, take care that you have an idea as to how the water is, and being close to the shore is recommended.
Apart from these, other things like practicing sighting, knowing the correct bilateral breathing technique, and taking full advantage of the draft, will help a lot. Finally, the most important ―if you have practiced hard and trained really well, trust your instincts and totally rely on your strokes to lead you ahead.