i think these are some good tips:

 - At least 15 creatures, most of them at low-medium mana curve.
 - You should have some spells or enchantments that boost all your creatures, like Overrun or HOTP (honor of the pure). The allies in Zendikar are a great modern example. Sleep is also very good because it practically gives you another turn to attack with all your guys.
 - Removals/combat tricks are always good. Mass removals are very good, just be careful not to kill too many of your guys.