oo...ya,i dont no how to set my state to make my Grand Cross become more strong and fast
For grand cross I would try to get an armour with the angeling card as it will prevent the splash back damage GC gives you (without this armour you take the unavoidable 20% of your HP plus some extra, It negates this extra).
Increasing your INT and STR will make it more stronger (Go more INT then STR). I'd actually suggest INT and DEX Since the longer you are casting GC the more damage you will take because during the cast your def is cut by 1/3.
If you can't afford an angeling card try getting a status armour (like Dark frame for example). I'd train at GH prison around that level with a GC build.
For a weapon a Bazerald or a Double hurricane [Andre x2] Haedonggum sword would be good.