How do you know which chicks to pick?

Okay, so after researching All Things Chicken for the past year, our coop is under construction and our local feed store will have my breeds of choice in a couple weeks. So here's my dilemma. When I go to buy, how do I look in a pen of peeping adorableness and pick the few I'm taking home?

First, I want healthy ones. I know better than to choose one that's dischargey or listless, but are there any other less obvious symptoms to watch out for?

Also, I want ones that have a basically friendly disposition. I've selected breeds that are generally friendly, but I wonder if there's a way to avoid the crabby or timid chicks.

Our chickies will be family pets first, and egg-layers second, so happy and healthy are important to us.

Thanks!

--Nikki