I think the best strat. for winning with Tzeentch is to invest in whatever regions possible early on to get your first upgrade-- Acolytes.
Now moving warpstones around, you have the ability to steal ruination from any other player on the board and determine ruination at will. Whenever Nurgle or Slannesh invest in a region for a couple of turns jump right in there with at least 3 cultist and 3 warpstones to complete runination. You will most certainly get 3 to 4 VP for contributing to ruination that round and a strong bid for first place. Also the more upgrades you get (and lucky OW cards) the more warpstones get placed, eventually you can work your way up to move 1 warpstone for every cultist you own. 6-8 cultist plus 6 warpstones equal ruination.
Furthmore, you can ruin Populous regions to block Nurgle and "trap" Noble and Hero tokens in ruined regions to thwart Slannesh. Khrone still will cause you grief, but nothing more than usual.