Two ends of a spectrum: All of the descriptions below contrast one pole of a spectrum with the other (external-internal or gross-subtle). In this way, the practices can easily be compared, while seeing the relative value of one versus the other. One form of practice might be useful at one stage, and the other more useful later on. 

Repetition with feeling 

One can recite a mantra solely as a mental process, somewhat like training a parrot in rote repetition. While this may help train the mind to be one-pointed, it is not nearly as beneficial as reciting the mantra with feeling. Recitation along with feeling is a deeper process that brings greater benefits. 

In either case, it is important to note that the use of mantra merely to repress emotions is not the intent. With emotional challenges, mantra can have a stabilizing effect while a person deals with those challenges in other healthy ways as well. 

Chanting internally 

Chanting mantra aloud can be a very enjoyable and useful process, whether alone or done with a group of people. 

After some time that process turns inward, and the chanting is done in the inner silence. 

Repeating itself 

One might initially use willpower to remember the mantra. This training the mind has a centering or balancing effect. (However, it is not a good idea to use mantra to repress, avoid, or escape from other thoughts and emotions.) 

Another approach is to sit silently, with attention inward, and allow the mantra to arise and repeat itself. It might take some patience, but this is a subtler practice. 

Notice that repeating with willpower is a form of expression, while allowing mantra to arise and repeat itself requires attention. (Expression and attention relate to the indriyas.)

The process of attention is more internal than the process of expression. Also, attention leads to concentration; in turn, concentration leads to meditation; and then, meditation leads to samadhi.  

At its own speed 

Some practitioners and teachers of mantra recitation intentionally see how fast they can recite the mantra. This can definitely create a groove in the mind for remembering the mantra. 

A more advanced or internal practice is to allow the mantra to come at it's own speed. Over time, the mantra will naturally shift in speed, sometimes moving very fast, faster than the mind might normally be able to recite. At other times, it will naturally move very slowly. 

Counting or not counting 

Counting practices can help to focus the mind and create deep impressions that have a stabilizing effect. 

A practice where a specific number of mantras is done over an extended period of time (called a purascharna) can be a very beneficial practice in clearing or purifying the mind. For example, one might do 125,000 repetitions over a few months. A larger and longer practice is called a maha-purascharna.

Yet, when counting mantras, awareness might tend to stay more on the surface level due to the external aspect of the counting. 

When the counting is set aside, the mantra can more purely shift to a deeper form of meditation, where attention is naturally drawn to the mantra as a single object of focus.  

Both practices, counting and not counting, are useful and have their place in sadhana (spiritual practices).

With or without mala 

In the beginning of using mantra, it can be beneficial to use mala or counting beads when remembering mantra (mala usually has 108 beads). By getting the physical body involved through the motion of the fingers, it can be much easier for the mind to stay focused. 

However, setting aside the mala, disengaging the use of the motion of the body (the karmendriyas) allows the attention to more purely go inward, past body and sensory awareness, following the mantra as it leads you inward. 

Both types of practice, with or without mala, are useful and have their place in sadhana (spiritual practices).

Four levels 

Mantra will naturally move inward through stages, if allowed. It is important to remember this, so as to not unintentionally keep meditation shallow when it is trying to move into deeper peace. 

For example, the word shanti means peace or tranquility. The feeling that gradually emerges is more internal and peaceful than is the repetition of the syllables alone. When the syllables drift away, one might then meditate on the feeling of peace itself, which is more subtle. Initially, this feeling might fade quickly, and be resurrected by again remembering the syllables of the mantra. 

Gradually, that feeling has fewer breaks or distractions, and becomes a somewhat constant, pervasive awareness. 

This eventually leads inward to a deep awareness that is the root of the sound. It somewhat defies description, but as a root of the sound, it is like a soundless sound of the mantra that is resting in silence.   

Mantra as a name of God

Some practitioners use as their mantra a name of God from within their religion, or as given by a teacher. 

At first the mantra or name might be used externally through repetition, chanting, or in song. 

Or, the name or mantra might be recited or remembered internally. 

Then, the name or mantra itself might drift away, as the grosser sound is replaced by a deeper longing or communion for what is behind the name or mantra. 

Mantra will lead 

Sometimes the mantra is naturally trying to lead attention into silence, and the practitioner thinks that mantra is being forgotten. There may be extra effort to then continue to recite, or internally speak the mantra. 

Deeper than this is to allow the mantra to naturally lead attention to its deeper, subtler aspect that rests in the silence. 

This leading process can be tricky in practice, as one might just be falling asleep. It requires a bit of practice and attention to notice the difference between drifting off into sleep and going into a deeper, quieter, more clear state of mantra meditation. 

This leading quality is one of the most important aspects of mantra practice. 

Speaking vs. listening 

A good way to understand this dimension is to think of songs you may have heard. Once those sounds are in your mind, they automatically arise, without any effort. 

Initially one may internally speak or recite the mantra. 

Later, the practice is more like listening to or remembering the mantra, than actively speaking. 

One may or may not literally hear an inner sound. It is the mental stance of listening or remembering that is being practiced here. It is somewhat like remembering a person whom you love. The name of the person may come and go in your mind field, but the memory of the person is not dependent on the presence of the name. 

(To further understand the significance of the difference between speaking and hearing, see the paper on the indriyas.) 

Dealing with thoughts 

Mantra can unwisely be used to repress ones thinking process. Mantra should not be used to avoid life and dealing with mental and emotional issues. At meditation time, one can easily get into an inner fight between the mantra and the stream of thoughts. This is not the best thing to do. 

Better than fighting, is to allow a period of time for inner reflection or internal dialogue to explore and deal with those thoughts and emotions. Then, it is much easier to remember the mantra as it naturally arises in the stream of the mind.  

Japa and listening

Some translate the Sanskrit word Japa as reciting or repeating, while others translate Japa as listening or remembering. One is an active process of expressing, while the other is a passive process of paying attention. 

These are two different approaches to the use of mantra (mantra japa). The process of actively reciting or repeating is more externally focused, while the process of listening or paying attention is more internally focused. 

The active process is easier to practice in the beginning, while the attention process is more internal and advanced.

Ajapa japa 

For the approach whereby mantra japa means actively repeating (noted above), this process might become automatic over time (like spontaneously singing a song you have heard many times). This automatic repetition is one form of the term ajapa japa.  

For the approach whereby mantra japa means listening or paying attention, that awareness might gradually become a constant awareness of the underlying feeling associated with the mantra. This is another, subtler form of the term ajapa japa. 

Where mantra japa means repetition, then putting a- in front of it means without repetition. Hence, ajapa japa is repetition without repetition (it is automatic). 

Where mantra japa means listening or remembering, then ajapa japa means constant remembering without the effort of reciting to cause that awareness.