What does it mean if the capability index is .08 and how can you increase the numerical value?
Add 0.01, of course!
Just kidding, but in the future, add some more context...
I'm assuming you are talking about process capability, in which case this has to do with how well a process can perform the function within your design specifications. There are many ways to increase the number, but not all of them are practical or cheap. Sometimes it's a simple matter of replacing a piece of equipment which has the lowest precision, it's also possible to go the other way and reduce the precision requirement of the process (say from 6 sigma to 4 sigma) though places don't generally do this if possible, as this can lead to quality issues.
I'm pretty sure that .08 is a dreadful index, pretty much saying that your process is not adequate for the desired production specifications...anyway,check wiki first in future http://en.wikipedia.org/wiki/Process_capability_index
This site goes into some nice detail on it in layman's terms:
Separate names with a comma.