I try to simply focus on the breath and empty my mind of anything else whatsoever. I started to do this whilst having acupuncture 6 months ago. 20 needles in the body from chi point in crown of the head to feet and everything in between - 45 beautiful minutes to 1 hour of forced immobility (or else one might lose a needle or two) does focus the mind somewhat.
I have also tried the following:
"I don't think" (all on exhale, inhale just watches the breath as the bellows fill). And
"zaaaaaaa- zen" (za-zen).
I also hear that counting each exhalation to 10 is highly regarded, which has already been mentioned. I have not tried that but I love the idea so I will (zazen).
Out of whimsy & to focus the mind on meditation even more, I bought a Yukata kimono to meditate â€“ in fact I bought two - one white, one black - both with the same inscriptions in Japanese, which is the Heart Sutra which contains a mantra. Alas I don't speak Japanese or the original Sanskrit. I'm still trying to figure out what I can use! But I'm quite keen to use this sutra's mantra - sutra purports to explain the meaning of existence and nonexistence. Enlightenment â€“ Life, the Universe, and Everything without recourse to the number 42!
And, of course, I'm going to try all the mantras on this post that all of you wonderful people find helpful â€“ thank you.