Thanks for the query.
Usually for natural conception at-least 40 to 50% motile sperms with 15 to 25% of rapidly motile sperms are needed.
So he can use some medicines to improve the motility for few months.
After that once go for semen analysis
If the motility improves, it is good. If not you can choose artificial methods like Intrauterine insemination
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429