I'm kind of a music nut. It helps me to think about a song, to sing it in my head, or hum to myself. The trick is to think of a song with a tempo that matches your horse's natural gait.
If your horse doesn't mind the noise, an electronic metronome can help too. Have a knowledgeable buddy set it to each gait, and write the tempos down for future reference. Most metronomes can be set to 4/4 time (walk), 2/4 time (trot), or 3/4 time (canter), and set from there to different speeds within each number of beats.
A stubborn horse walks behind you, an impatient one in front of you, but a noble companion walks beside you ~ Unknown