Dhyana is the advanced stage of Dharana and it the 7th step of the Ashtanga yoga, it is a state of mind that emerges spontaneously.
All the meditation techniques are meant to lead to Dhyana on the condition that they are practiced fervently and on a regular bases. Do not try too hard to control the mind, if you try this, it might happen that you can control your thoughts but not necessarily your mind. Most people do not know their mind very well, it is like looking to an iceberg: most of it is under the waterline and only what is above the water is known to us.
There are different techniques to help us go into the state of Dhyana. Most techniques encourage the meditator to control all the activities of the mind, but this can cause a conflict in the mind. The Tantric philosophy (of which Yoga is the practical side) believes in "letting the mind have it's way and not the intervene". This philosophy advises to observe the mind and in this way get to know it well.
In the book "Sure ways to Self-Realization" written by Swami Sayananda Saraswati, you can find and interesting story on page 70 that compares the human mind with that of a wild horse.
Befriending the mind
Once upon a time there live a king who had a most beautiful but rampantly wild horse. The beast could not be tamed. The king decreed that he would handsomely reward anyone who could subdue his stallion. Prompted by the thoughts of wealth, many people came. Each man tried to match the horse with strength, but non was strong enough to overcome the animal by mere force. Even the mightiest were thrown off or injured. Soem time passed until on day the king saw the horse meekly obeying a newcomer's instructions. The king was amazed, and demanded to know how this man had succeeded where so many other had failed. The horse tamer replied, "Instead of fighting your stallion, I let him run freely to his heart's content, following his own impulses. Eventually hi became fatigued and submissive. It was than no problem to befriend your horse and gain command."
It is the same with th emind. If We fight and wrestle with the mind, we will never achieve mastery over it. The method to adopt is similar to that of the wise horse tamer - let the mind follow its impulses and tendencies without restriction until it becomes ready an willing to accept our authority. Give the mind free rein. Do not suppress it, but merely watch and get to know it.
Most people who practice meditation try very hard to control the mind, but they do not know the mind, its mysteries, idiosyncrasies and its potentialities. They are only controlling their own thoughts and thoughts are not the mind. What they know of the mind can be compared to what we can see of an iceberg, most is below the waterline and only a little above.
Dhyana is meditation, meditation is a state of mind of to be with what is. It is most definitely worth being reached. If you have not experienced it yourself it is hard to understand this description.
Meditation is in essence to observe without judging in a relaxed way. You are just a spectator. You will experience the connection of your inner center, the 'silent middle", so that you can live more in the here and now.