To concentrate, first you have to make yourself relax, do not think it is complicated.

Then, start to focus on your breathing, in and out, just in and out, imagine you breathe in the positive air and clean your mind and body, then imagine you breathe out all the unnecessary negative thoughts, emotion.

You cannot concentrate is because the other senses of your body is not collaborate together in this activity, like you are thinking something else, listen what is going on outside your room. So you have visualize the breathing activity (mind), listen to your breathe in breathe out (ears), just let your senses focus in this activity.

I learned it from YouTube lol. I practice few times only, and its quite fun . Lately, i did stop a while, because i can't really relax due to work and stress. Once i stopped, its quite hard to get back the feeling, its like i lost the momentum.