Chanting is a communication with the universe.
When Nichiren Daishonin chanted the first Nam-myoho-renge-Kyo on April 28, 1253, he was facing east, towards the rising sun.
For us, we can't possibly do that without inviting disapproving glares from passersby.
Hence, we do our chanting in the privacy of home. Face the wall and imagine the Gohonzon (the object of worship, specifically, the letter "妙") in front of us as we chant.
And while chanting, we do the following:
1. Our body (身): we sit in a posture of supreme respect, putting our palms together, holding the beads,
2. Our mouths (口): we utter the invocation "Nam-myoho-renge-Kyo" as clearly and crisply as our mouth can possibility pronounce each word, and at a suitable loudness.
3. Our mind (意): we think/visualize the prayers we want to be answered.
The moment you feel that it is boring, check on all the numbers 1,2,3 again; Very likely, one of the three things is amiss. The tell-tale sign that our concentration has drifted is when our invocation becomes slurred and we end up mumbling instead of chanting. That is when we need to refresh our determination/prayers by chanting crisply.
From my personal experience, concentrate on pronouncing each and every syllable of the chanting clearly, by exercising your entire mouth (ie. don't mumble) and you will really come to enjoy chanting, and you can even chant for long hours!
By Chang Cheng Liang