If you want to quickly enter samādhi, you can practice preliminary guidance.

Lantian's Meditation and Contemplative Practice Diary 

Day thirty-one of observing the breath. Before sitting, I gave myself a suggestion: during today's meditation, I would no longer think, would reduce thinking, would also set aside everything unrelated to meditation, and would focus my mind only on the breath. After sitting down, I adopted active deep abdominal breathing. Today I placed my attention on the lower abdomen; slowly the abdomen began to feel somewhat warm. After about five minutes, a subtle sensation of qi gradually arose, deep breathing became easier, the muscles of the lower abdomen twitched, and it felt as though the qi mechanism was about to be activated. After about ten minutes, I stopped the active deep abdominal breathing. 

Then I began observing the breath at the nose. Today, unlike the previous few days, I did not switch to natural breathing, but instead used consciousness to slowly guide the abdominal breathing. After just a few breaths, the qi mechanism in the lower abdomen was activated and it went directly into deep abdominal breathing. At this point, my thoughts were placed solely on the breath, while simultaneously perceiving the sensations throughout the whole body, minimizing analytical thinking activity. Because the mind was concentrated, the breathing was natural, deep, and subtle, and the amplitude of the breath was even greater than during active deep breathing; the airflow passed through the chest, upper abdomen, and middle abdomen, reaching all the way to the bottom of the abdomen, until the end of the sitting. 

During the breath observation, the mind was concentrated, the object of contemplation was clear, and the breathing was even, deep, and subtle. In the middle portion of the sitting, I suddenly felt a very distinct cool sensation on the outer side of the right hip; before the end of the sitting, the right ear had a continuous sensation of coolness (the right ear had been hot and swollen for two months due to internal heat earlier). 

Assessment: Cultivating meditative concentration can be done as a preparatory practice, actively adjusting the state of body and mind and guiding it toward a state relatively suitable for entering concentration; then the mind will settle down and enter concentration. In active guidance, the mind's attention is focused on one thing, interested only in that one thing, screening out other objects of contemplation—this in itself is wisdom, and it is also concentration. In the process of cultivating concentration, one should fully exercise wisdom, using wisdom to lead into concentration, combining concentration and wisdom; entering concentration will then be very fast. Some people, when cultivating concentration, force concentration without using wisdom, and as a result find it very difficult to enter concentration. Others only use the wisdom of the mind consciousness to analyze and deliberate, yet never enter concentration. Both of these modes of practice are one-sided; they do not follow the Middle Way and cannot give rise to meditative absorption (samādhi).