Would like to improve at playing Skarner

(Hopefully in posting in the right place this time...) I've been playing Skarner recently with much success(Jungle and Support), but I have had some pretty disappointing games where I felt I didn't help the team enough, or I didn't use an early lead effectively. I've been playing with a utility mindset and building mostly full tank and using mostly utility masteries starting with 10% CDR. Any tips or advice would be appreciated, it's not that I've been losing a lot or anything, would just like to improve my play. Also should I be using 21-9 or 9-21? I currently used 4-5-21 as jungle with the same for support with a few differences. Also I am currently only Silver 3.