There are many ways to meditate, but one of the most effective - especially for those who find stilling the mind incredibly challenging - can be sitting to a mantra.
A mantra is a phrase or word that is often, but not always religious (or spiritual), repeated continuously.
The Universal mantra 'Om' is often used - others include 'Om mane padme hum' ('the jewel is in the lotus' or 'Om nama shivaya' (a chant to the Hindu god, Shiva).
To practice mantra meditation, sit with your spine straight - either on a cushion on the floor, with cross legs, or on a chair if sitting on the floor is uncomfortable.
If you can, try and get used to sitting with cross legs on the floor (in Easy Pose, or Sukhasana) as it allows the spine to strengthen and the hips to open.
Take some slow, deep breaths and fall into stillness. Encourage the mind to settle but don't become frustrated when it shoots off in all directions - simply bring your focus gently, without judgement, back to the breath.
When you notice your mind becoming more focused, start saying your chosen mantra to yourself repeatedly, in your mind. Repeat it softly, in a rhythmic fashion. Simply do this for five or ten minutes, or more if you'd like to.
Over months and years, our minds can be trained to become more self-disciplined. For Westerners unaccustomed to focusing on stillness, mantra meditation is a fine introduction to the practice of quietening the mind.