This is a common problem for even advanced players. Unfortunately playing with hands together is 37 times more difficult than with hands separate. This is not a technical problem. It is a co-ordination problem. Although some people may say that co-ordination is a technical problem, it is useful to treat it separately. So work on technique with hands separate. Once you have mastered the technique (that is, you can play hands separate perfectly and subconsciously) you will be ready to tackle the co-ordination between hands.
The problem here is the same as when you try to rub your tummy in a circular movement and tap your head at the same time. Try it!
You will see that one hand’s movement keeps interfering with the other hand movement. They both want to move in sympathy. How do you deal with this?
First understand the natural sequence of events: mind (brain) – nerves – muscles. The mind orders, the nerves transmit the orders, the muscles obey. To deal with sympathetic movements you must have a clear mental image of what is it that you are trying to do. Then you must inhibit the sympathy at the level of the nerves. Most people try to deal with this at the muscle level and as a result get more and more tense. It has to be done at the nervous level. How do you do it. I cannot tell you. I don’t know how to tell you. But it doesn’t matter, because you already know how to do it. You are already accomplished in the most amazing feats of co-ordination. Like walking.
Ok. Now for some practical advice. Start rubbing your tummy. Now you are going to pat your head. But don’t start patting like crazy. Do one single pat and stop. Meanwhile keep rubbing your tummy. Your aim is to not let that single pat disturb your tummy rubbing which should be even and regular. Investigate how you can achieve this. Remember that it is not by working on the muscles – so if you are tensing or loosing the evenness of the rubbing movement you are using the (wrong) muscle approach. So try that for a while: rub the tummy and “drop” single pats on your head. When you feel confident start doing two pats. Then three, until you can pat your head and rub the tummy at the same time. Then reverse it. Tap your head evenly and regularly. Then do one single circle in your tummy. Again the aim is to not let that single circular movement interfere with the tapping. Remember, we are talking nerve inhibition here, not muscle tensing.
Have you got it?
Playing with hands together follows exactly the same principle but it is more complex because you have more moving parts to co-ordinate (fingers, hands, wrists, forearms, arms, shoulders).
So – exercises in which both hands do the same thing will be almost useless here. (Sorry, Ilovemusic) These exercises foster sympathetic movement and hand dependence. They are like tapping your tummy and tapping your head. You want independent movement and hand co-ordination. So make sure you really mastered each hand’s movement before trying to join them. Then put one hand – say, the right hand - doing the complete movement – the whole sequence of notes – and “drop” one single note of the left hand. Repeat as many times as needed to get the knack to drop the left hand note without interfering with the right hand movement. Then add the second note. Then the third. Until you can play the whole passage. Then reverse by playing the left hand and dropping the right hand notes. And always remember that you are targetting the nerves, not the muscles.
Try it and tell us how you are coming along.