Okay, this is basic one, but I wish someone would have told me you HAVE to have a lid on your brooder or they will fly out and never be able to get back in. When we first got them we just stuck them in a small tub inside for a couple of days to get a more permanent brooder set up and they kept flying out and pooping on the carpet of the room we had them in! So, for new chicken people- lid on brooder, even indoors.
Second thing, don't raise ducks with the chickens. Set up two separate brooders for the first few weeks. Not to say that it's impossible, because it isn't, but it's a lot less work. Not knowing any better we tossed them all in together- which was fine, no fights or anything, but the ducks squash the chicks to get to food and water, and play in the water and get the brooder SOAKED. Although baby ducks shouldn't be wet any more than chicks should, really, they can still handle it better than chicks can.
Also, do your research on the breeds you want before you go pick them up, or get them, and memorize what they should look like at a few days old. When we went to
TSC the guy told us that even though the chicks were in the red pullets bin, he knew for a fact they were RIRs. We believed him and got 6. A couple of weeks later we realize.... hey! these aren't RIRs; what are these? We actually got 6 red stars, which isn't a big deal, we love them anyways. But do your research on the breed before you take the advice of just anyone who works around the chicks.
I'm still a newbie myself, but these are the main things i've learned in the past month...wow, I've had chicks for a whole month and none have died! That's a better track record than with my garden.