How to divide a Group ?

How is the best way to divide a group ?
eg : my main group is 1 thru 24
divide by 2 : "Group" "Next" select 1 > 12 "Group" "Next" select 13 > 24
divide by 3 : "Group" "Next" select 1 > 8 "Group" "Next" select 9 > 16 "Group" "Next" select 17 > 24
thank's