Saint Theophan advises in the following way:
One does not have to do many prayers. It is better to perform a small number of prayers properly than to hurry through a large number of prayers... I would consider the morning and evening prayers as set out in the prayer books to be entirely sufficient... Just try each time to carry them out with full attention and corresponding feelings... Prayer does not mean that we just recite prayers, but that we assimilate their content within ourselves, and pronounce them as if they came from our minds and hearts.
When you stand at prayer, be careful to keep your mind from drifting and your feeling from coldness and indifference... After you have recited each prayer make prostrations, as many as you like, accompanied by a prayer for any necessity that you feel, or by the usual short prayer...
You must also maintain prayerful attention towards God throughout the day... it is good, very good to memorize several Psalms and recite them while you are working or between tasks, and doing this instead of short prayers.
Go to bed with a short prayer on your lips and fall asleep with it or recite some song.
You may limit the entire prayer rule to just prostrations with short prayers and prayer in your own words. Stand and make prostrations, saying “Lord have mercy,” or some other prayer, expressing your need or giving praise and thanks to God. You should establish either a number of prayers, or a time–limit for prayer, or do both so that you do not become lazy.
The essence of prayer is the lifting of the mind and heart to God; these little rules are an aid. We cannot get by without them because of our weakness.More on prayer and a prayer rule
Reference: The Spiritual Life, pp 204-209