I'm pouring a 20'x30'x 6" thick floor and plan to reinforce it with 3/8' rebar. What's the best rebar spacing?

2 foot center, make a grid with it. Tie wire it all together you dont have to tie wire every one just enough so it all comes up at once while you are pouring.Lift it as you pour or put broken chunks of brick under it.Dont pour it at a 2 or 4 more like a 6 or 8.Youll kill yourself and all your help and probably lose it. Pour at a 6 or 8 all the time never had a problem. Tell the ready-mix plant what slump you want.