That's what I did:
Play the gen. Than u have to understand all of the time u died why u died. 
Is it because of your playstile? You are totally stupid? Make a build that supports stupidity.  - go for IF and Shield
Is it because you die by arrows? Get more ATH and shields
Is it because you do too less dmg? Get more str/more ATH
............... 
That's how I made my builds, so I allways wonder what the build of somebody is. 
His build will be never urs (or at least ordinary). Cuz ur build has to be made for u. 
I did allways getting more sp in what I died for. So too slow? more ath. Too less dmg ...
But with a build of 21 21 things should go right, you could get more agi/str but a balanced cav build is absolutely recommended from me!
But for sure, if you are a real tryharder, get the highest build u can. I know really good cavs that play with 24 24 
