In general it is possible to attain mental quiescence by visualizing any type of object; but for a Buddhist it is especially beneficial to meditate on an image of a Buddha. Doing so helps one to accumulate merit and purify mental obscurations; later, it greatly aids one in tantric practices involving the visualization of deities. Further, such practice encourages one to reflect upon the fully enlightened beings and their virtues. This image should be visualized about an arm's length in front of you, either at the level of the eyebrows or of the heart. The former method should be used by those especially prone to mental dullness, and the latter by those prone to mental agitation. Or one may visualize oneself as appearing in this form, but only if one has had the proper initiation. This image may be the form of Buddha Shakyamuni, or any other manifestation of the Buddhas. On the other hand, if one is more inclined to meditating on a formless object, one may develop mental quiescence by concentrating on the mind, as explained in Je Tsongkhapa's Small Exposition of the Stages of the Path.
Although many objects of concentration are discussed in the Buddhist scriptures, one should not hop from one object to another. Rather, find the most suitable one for yourself; then persevere with that until mental quiescence has been attained. As the sage Ashvagosa stated:
After placing the concentration on one object during meditation, if one moves to another, single-pointedness will not be attained. For example, one could not make a fire by rubbing sticks together if one continually changed from one stick to another. Further, just as one must continue rubbing uninterruptedly, while mental quiescence is developed it is best not to engage in any other activities, except the natural functions of eating, sleeping and obeying the calls of nature. If one frequently becomes exhausted from the practice and takes a rest from it every few days, mental quiescence will not be attained.
To visualize a Buddha image, first carefully observe the actual Buddha image on which you wish to meditate. Then, when you are quite familiar with it, mentally visualize or imagine it. If a general, rough image of this form appears to the mind, the object has been found. Losing awareness of it is the second of the five faults, namely forgetting the oral instructions. The remedy for this is the fifth of the eight factors, mindfulness. As with grasping a rosary, one's hold on the visualized object should be firm yet relaxed. Individual people naturally have varying degrees of mindfulness; this influences the rate at which they can attain mental quiescence. . . .
A meditator who has accomplished the six preparations for mental quiescence must recognize its five faults, as described in The Full Investigation of the Centre and Extremes. The five faults are laziness, forgetting the oral instructions, sinking and excitement, non-application and finally application. Further, one must apply faith, yearning, suppleness and effort as the remedies for the first fault, mindfulness for the second, discriminative alertness for the third, application for the fourth, and equanimity for the fifth. Thus one applies the eight remedial factors.
If one knows how to distinguish between the nine concentrative states, knows how they are attained by means of the six forces and how they are included in the four types of attention, it is said that one can attain faultless concentration with ease.
Here is an illustration based on a verse in the Essence of the Middle Way.
Here comparison is drawn with taming a wild elephant. The illustration shows the nine stages of this process, corresponding to the nine concentrative states: namely, mental placement, continual placement, patch-like placement, close placement, subduing, pacifying, fully pacifying, single-pointed application and spontaneous placement. The way these nine are attained with the six forces is as follows. The first state is attained by the force of hearing the guru's oral instructions, the second by that of thought, the third and fourth by the force of mindfulness, the fifth and sixth by that of discriminative alertness, the seventh and eighth by that of joyful effort, and the ninth is attained by the force of complete acquaintance. The way these nine are included in the four types of attention is thus: the first two states are the occasion of tight attention, the next five of interrupted attention, the eighth is the time of uninterrupted attention, and the ninth of spontaneous attention.
After progressively achieving these nine states by such means, stable suppleness and mental quiescence are simultaneously attained. This state is included in the initial state of the first mental absorption.
In this illustration, an elephant is depicted as representing the mind. In other such illustrations, a horse or bull is drawn; but there is a special significance in using an elephant. A wild one can be very destructive, having the power to destroy crops, villages and human life. But if it has been tamed, its might can be directed to many constructive tasks for the benefit of all. Likewise, an untamed mind can bring immense harm to oneself and others, but if it has been subdued, it can be employed in activities that result in ever-increasing joy in this life and hereafter.
The black colour of the elephant represents dullness and sinking; and the elephant wildly follows a monkey, which symbolizes agitation. The black colour of the monkey represents excitement. These two are followed by a monk representing the meditator. In his left hand he holds a rope symbolizing mindfulness; in his right, a hook stands for discriminative alertness. The flames along the path symbolize effort. At the beginning of the path, they are very strong; but they dwindle as one progresses along it. This indicates that very strong effort must be applied at first, but not so much later on. The six curves in the path represent the six forces. The illustrations of fruit, cloth, a conch and so on represent the five sensory objects. These are a main cause of excitement; so the mind must be withdrawn from them during such meditation. The rabbit on the elephant's back represents subtle sinking; it is chosen because it is very difficult to recognize when it sits quite still. The monkey in the tree symbolizes agitation towards virtuous activities, which are represented by the fruit. This indicates that the mind should not be drawn to other Dharma activities during this meditation; though they should, of course, be followed at other times.