Meditation can be considered a Scientific technique or practice that involves concentrating on God. By Meditation we mean "Dhayana" or Contemplation, it is a fully conscious process or an exercise of the will.Over time, the number of random thoughts occurring diminishes. More importantly, your attachment to these thoughts, and your identification with them, progressively become less. He who practices meditation without ethical perfection, without the practice of Yama-Niyama cannot obtain the fruits of meditation. Purify your mind first through the practice of Yama-Niyama. Then practice regular meditation. Then you will attain illumination. The vedantic aspirant who believes in the existence of the divine may at the beginning meditate on the physical form of some holy deity or personality or a symbolic representation of the divine first associated with time & space & then without these limitations.Advancing further he may meditate on the Heart or Middle of Forehead.Meditation on OM with Bhava and its meaning removes obstacles in Sadhana and helps to attain Samadhi. "Raja Yoga is a practical guide for gaining control over the mind. The second sutra (of Patanjali's Yoga Sutras- Ed.) states, "Yogas chitta vritti nirodhah," or,"The restraint of the modifications of the mind-stuff is Yoga." Every thought, feeling, perception, or memory you may have causes a modification, or ripple, in the mind. It distorts and colors the mental mirror. If you can restrain the mind from forming into modifications, there will be no distortion, and you will experience your true Self." Meditation must have some definite positive spiritual content. Very often the mind of the modern man revolts against the idea of rigid formal meditation.He says, " Why should we busy ourselves with taht? Haven't we enough drudgery in the world? So why should we follow practices whihc do not appeal to us? We want Absoulute, so what is the use of Japa, divine attributes or divine forms? Let us reach the absolute.Let us worship the divine "in spirit & in Truth!" All this, no doubt sounds very grand & highly spiritual,but as soon as we come down to actual life we finnd taht this kind of thinking does not produce anything at all.Mostly such people are dualists as far as  their own actions in daily life go.How many people really do it?--for most peole it means just hazy thinking & acting in a way that has no connection at all with the spirit or Truth.One needs to intensify our meditation & pay more attention to our quality rather than quantity of meditation. Absentmindenness is a sheer waste of time.

There are various types of meditation - prayer is probably the best known, but there is also TM (Transcendental Meditation), mindfulness meditation, and from the Eastern tradition, Zen meditation, Buddhist meditation, and Taoist meditation. 

Retention of Breath(Pranayama), Brahmacharya, Sattvic food, seclusion, silence, Satsanga, not mixing much with Worldly people are all aids to concentration on god or Meditation.Never miss a day in meditation. Regularity is of paramount importance. When the mind is tired, do not concentrate. Do not take heavy food at night if you wish to meditate.The cravings of the flesh, our desires,usually stand in our way of Real Religion.The Sham thing we ordinay see in life, going to places of worship & hearing religious instructions here and there & then doing just as one pleases is not true religion........By Shri Rohit Anand Ji ....Learn Meditation