In general the more you can reduce the temperature of your testicles, the better they will be able to produce sperm. Doctors recommend “loose fitting” clothing to help promote air circulation in that area and thus keep the temperature down. Try boxers instead of briefs, relaxed fit instead of skinny jeans, etc.
Laptops generate a lot of heat. So despite the name, try to keep the laptop off of your lap to reduce your heat exposure.
Same goes for cell phones. Try to keep them out of your front pants pocket when possible. Cell phones present another potential risk due to radiation and wireless signals. The jury is still out on this one, but some studies suggest the radiation from mobile phones can be damaging to the DNA in your sperm.