Based on the previous question where 85% of people had found less than 100 caches it's not surprising that most people have only placed less than 10 caches.
Cache Karma is the ratio of number caches placed versus the number of caches found. In other words when you find a cache you are benefiting from the work of another geocacher. So to contribute to the community you should place a number of caches in proportion to the number of caches that you have found.
The great thing about placing caches, and in particular, good ones are the positive comments that you receive when people write their logs.
So be creative and get out there and place some high quality caches.