well, i don't know everything, but i do know that the man should stop smoking, maintain a healthy weight and diet, avoid heat and tights as they really harm the sperm, so no sauna, no steam baths, no long bike rides.
hope others may add more useful points.
Also ejaculating to much lowers the sperm count so cut down on sex, like to every couple of days or so
cut down on oral or intimate contact. and or masturbation. and then those little swimmers will be fierce. Lol. seriously. good luck
Taking Zinc supplements can improves both sperm count and testosterone levels.