The ability of bringing up the meditation object of concentration to the point of access concentration just before absorption involves the building up of the mental factors of concentration skilfully, so that it becomes powerful enough to fall into absorption.
Some important factors in development of deep concentration are given here:
Mindfulness being the main controlling faculty of the mind is of course indispensable. It brings the mind to the point of concentration skilfully. Besides it guards against defilements and extraneous thoughts. Then it causes us to take the appropriate action to remedy it. It also keeps the mind flexible, workable, soft, and so on. Therefore there must be plenty of mindfulness at various depths. It will, however, have to be that suited to the tranquillity form of concentration and not the insight form. Comparatively in tranquillity meditation, the concentration faculty is much stronger than the energy faculty and so its unique balance has to be maintained. It has also to be continuous and as a result, it would be advisable for many to set up a strong grounding of mindfulness through various satipatthana exercises before one embarks on intensive samatha bhavana.
Right concentration is often referred to as concentration detached from the five senses. We can understand this if we know that our object is solely that of the mind door. Its concentration is that above the five sense doors. If we still have rampant cravings for sense pleasures, we can never get near the absorptions. However if one is really detached, then it lifts one off from the valleys of the five senses. Detachment has the power to remove the bondages that tie us to the lower worlds. When metta comes with pleasantness and joy, the detached attitude is an important consideration.
Patience is the opposite of impatience or anger which is associated with agitation. If we preserve patience, our mind by itself will calm down. In this case, patience is synonymous with the undisturbed aspect of tranquillity. It can remain with the object for longer periods of time, for with non-anger there follows equanimity, another factor of concentration.
Texts also inform us that to guard the concentration, we need to take into consideration the seven suitabilities. These external things are
2. village where one seeks for food
6. season, and
We can consider how these can influence our concentration and hence select the one which is conducive.