The best places to fish an ant pattern tend to be near the bank. If you can find a wash out, or a back eddy where the water has washed away some of the earth & made a nice hole, you should float your ant fly through there. Ideally, these places would have high over hanging tree branches above the water. Ants climb out on these limbs & fall off, into the water where waiting trout eat them. It's a good deal for the trout, too as these spots have shade from the hot summer sun & cover in the bank or roots of the trees (if they jut out into the water).
However, you don't need the trees to find ant-eating trout. Even in streams that flow through open meadows or cow pastures, you can still find ants on the water. Anywhere there's some taller grasses growing right up next to the water, there's a chance that ants will have fallen into the stream. Hitting these spots is a pretty good plan.
Fish these ant flies just as you would any other dry fly. That means a nice, drag free drift. You're going to have to adjust your leader & tippet, especially if the water is low & clear. Up stream fishing is also a good approach to use.
In addition to using the ant as a dry fly, you can also fish it as a wet. However, I've never had a ton of luck doing this myself. I almost always prefer to fish an ant as a dry. Still, if you do fish your ant as a wet make sure it rides high & just below the surface of the water. When they're feeding on ants, trout are almost always looking up.
Ever watch an ant that's fallen into the stream? Do it, you'll learn a lot. They try to kick & swim. They usually don't have enough mass to break through the water's surface, so they kick & try to walk across the water. It's almost always futile on the ants part, but it's the movement they make that you want to study. Try to imitate it a little with your fly as it you fish. Get it right & it could be the key to success.
One more thing about ants: they come in many different sizes. Even in your own back yard, I'll bet you could find a few different sized ants. So make sure you bring a bunch of different size ant fly patterns with you to the stream. You never know which size of ant is going to be on the menu for the trout on any given day.
Tying a basic ant pattern is pretty easy. With some practice even a beginner can whip out a dozen or more in no time. Below is a pretty good video showing you how to tie a basic black ant pattern: