The most common BAD advice given to young hitters that is absolutely incorrect is the "Get Your Elbows UP!"

This advice is heard at almost every little league game ever played usually by parents or grandparents in the stands. Many times it is even taught by uninformed coaches that heard it their entire lives. One such coach told me that he was familiar with the debate between elbows up and elbows down. The problem with that is that there is no debate among people that really know what they are talking about. No college or professional hitting coach will tell you as a common rule that a good hitting stance includes keeping your back elbow up or your front elbow up or both elbows up, referring to the elbow being at a 90 degree angle(plus or minus) to the body.

Then what is the correct form?

Elbows Down
Many people call the correct position "elbows down" where the forearms form an “A” or an upside down “V”. The elbows should be in a relaxed, down position and out away from the batters body. I wasn't specifically taught this correct form until I was 16 in American Legion. My coach played in the Majors and in college where he started at catcher and batted cleanup. He is currently coaching baseball at the college level. Needless to say, he knows what he is talking about.

Developing a Stride: Many aggressive young hitters have a bad habit of striding too far probably because they think the bigger the step, the bigger the hit. This is incorrect. Instead, the should take a controlled step that might be 2 or 3 inches from their regular stance. Overstriding can actually make a batter swing under the ball and either hit pop-ups or entirely miss the ball.

Some coaches say to not worry of teaching a stride and just suggest a wider stance while keeping a little wiggle in their butt. I personally like to teach kids to use a little rythem and transfer the weight from back to front foot. I teach a little timing or rythem step where they almost cock their front foot and then squash a bug with that same foot. Another bad habit that kids do sometimes is step with an open stance which loses all of that power in a batters hips.