The first step is to read the pitcher. Many pitchers at the youth level give away the fact that they are throwing a curveball before they even start a motion, ie. they dig around in their glove a lot, trying to find the right seams.
Second step is once the motion starts, see if there is a change in the arm slot. This is something that cant always be done, but especially later in the game, it should be recognizable.
Third step is one an old coach taught me, and takes a trained eye to see. Different pitches have different spins, and because of the spin, a red dot is created by the laces while its thrown. If you train yourself well enough, the red dot can be seen in time to know what pitch is coming. A red dot on top means fast ball, and anywhere else on the ball is something off speed.
If either of these steps lead you to believe that you should be anticipating a curveball, then follow the next steps. While I say ANTICIPATING a curveball, you should never SIT on a curveball. As a batter, you look for a fastball first, and adjust to offspeed pitches.
So if it IS a curveball being thrown to you, the best thing to remember is DO NOT LUNGE. If you are lucky enough to hit the ball, it wont matter because it should be an out. If you see the curveball, sit back and wait for the ball to reach you, and trust your hand speed. If you have slow hands, theres only so much I can do to help you. But one of the hardest things for younger batters to learn how to do is wait on pitches, especially off speed pitches on the outer third of the plate. If a pitcher hangs one on the inside or over the middle, go ahead and just blast it. If its on the outside, let the ball travel deep, not everything needs to be hit in front of the plate, and slap the ball out into right field.
Thats as much as I can put in writing about hitting a curveball.