Find a word that has a positive appeal to you. It can be love, joy, or peace, but any other word that gives a similar positive feeling works. Avoid using names as it might cause you to think of the person instead of focusing on the word. Just use a simple, positive word that you like.
Close your eyes. Calmly repeat the word in your mind over and over for 10 minutes. If any other word or thought enters your mind, reset your 10 minutes and start with your word of choice again.
Practice this exercise until you can focus on repeating your word of choice for 10 minutes straight without interruption before going to the next exercise.