Use the "rule of four".
Bard, Rogue and Red Dragon Disciple all come from the 3/4 Base Attack Bonus (BAB) catagory. For every four levels their attack bonus goes up three points pre-epic. To maximize your BAB you should take these classes in groups of 4. For example: Rogue 8/Bard 4/RDD 8 would give you a BAB of 15; but a Rogue 10/Bard 5/RDD 5 would only have a BAB of 13.
I hope this helps.
