How Can I go faster to reach better position in karma, i think used all the recommendations?
There is nothing you can do, continue to complete tasks on time, and that would be the point of Karma, to help you complete tasks. Helping on these forums can also grant some karma points.
Is there a benefit of having large karma?
Yes - the feeling of great achievement ;) Other than that, there are currently no tangible rewards, but we may consider it in the future.