You can use the early levels for team and character building. The earliest adventures are mookish -- what else can you send the 12 hp fighter and his equally fragile friends to do? The wizard, who almost everyone on these boards thinks is the heart of Tier 1 invincibility, gets to say, "I cast my 1 magic missile I get today and then go home. See you guys tomorrow."
Gangs of thieves and bandits are nice for getting things going. Mysteries are good, since players need their minds more than their sheer destructive power to win the day. By levels 3 thru 9 (my favorites: the party isn't invincible but doesn't have to run away from a half dozen giant rats either), the group can bond over background color. If the wizard's family was killed by Ogres, let him go back with his new friends and settle the score. Evil half brother steal your estate, cleric? Let's go back and see if we can "persuade" him into changing his mind. Lose a friend down that old tunnel? Let's take a look.
Encourage the players to give you these threads when they draw up the characters. Some are plotting their way to the Titan/Pixie dragon-wrought 20th level abomination killing machine but you need to draw them back to the character: why that guy is interesting to the player, why the character will be interesting to others, and why pick this guy over some other concept.
The players can give you everything you need to fill in the lower levels. My .02.