Concentration - Relaxation balance
If you remember using a microscope or telescope in science class, you will realize how importance of patience needed to tune lenses to obtain a clear picture. It's similar to when we tune a radio or used to tune televisions to receive a channels. We are used to being careful to tune devices to get a precise result.
When you meditate, you need to be concentrated and relaxed at the same time. For relaxation, it's depends most on your body. Please relax your body to the maximum. The more you can relax your body, the better your meditation will be.
For concentration, it's all about your mind. It means your mind needs to concentrate on something but with a minimum of effort. You cannot let your mind have nothing at all to do because without any concentration, your mind can be restless easily. The 'monkey mind' comes when we have nothing to do. You need a little something for your mind to be drawn to.
The mind will be still only when you can relax your body to the maximum your body and concentrate your mind to the minimum. You do only this. Relax your body first, then bit by bit you focus your mind gently and peacefully on the center. If you do it well, you will enjoy it and feel that meditation is easy.
If you are not mindful enough when focusing your mind then you might lose your focus, or as we say, become too relaxed. If it's very easy for you to fall asleep or have a wandering mind then your mind is not yet well tuned.
In the opposite way, if you try to concentrate too much by forcing your mind to see a mental object or hear a mantra, you will lose your comfort bit by bit. Once you feel uncomfortable, your mind becomes restless again.
To guide the mind to be still with the minimum mindfulness effort of and the maximum body relaxation is considered the art of meditation.