What can I do to improve the health of my sperm

Try drinking more water and adding more fruit and vegetables to your diet if you don't already do so.

Thick bodily fluids of any kind - including ejaculate fluid - can sometimes be a sign of dehydration, so if your urine is dark/not clear, it's probably time to add more water.

Adding fruits and vegetables and drinking less coffee (if you drink coffee) and eating less meat (wouldn't really recommend it unless you are already eating little meat) can improve taste... so I've heard.