That depends on your purpose. For relaxation you can use meditative music and staring in the flame of a candle. For self-development, finding your hidden potential and your inner self, for discovering a new meaning in your life - these things ask for a type of meditation in which you concentrate on a very high idea. Infinity, love, inner peace, or, if that feels good for you: the cosmic consciousness (who has these qualities).

If a great spiritual person gives you a mantra, (a spiritual sound that you repeat during meditation), and that mantra has the mind-expanding meaning mentioned before, then you have a very powerful tool for self-development.

Unfortunately there aren't many really great spiritual people that can give you a mantra. But if you find an advanced student of such a 'master', he can serve as a channel and relay the spiritual energy that that the master put into the mantra, to you.

NB. Be very careful before you accept someone as your teacher. Unqualified teachers (often with good intentions!) are easy to find, good teachers are scarce.

A book that teaches you a mantra is not very effective, books are not living channels and most of the original spiritual energy of the mantra doesn't reach you. Apart from that, the book can't see what you need on your individual spiritual journey, like a good teacher can.