Register early. You will change your mind and find out all kinds of new things during the process of registering. Do not wait until a month before your showers to do this. You will regret it.
Babies “R” Us might be what Hell is like. Just know, the first time you go to Babies “R” Us (BRU), you will probably be so overwhelmed you will cry. It is a horrible, yet necessary, place. Get used to it. It gets easier.
You CAN get everything at BRU, but some people are scared of that place, so register somewhere neutral, like Target. I know that I, personally, would never go to BRU for a shower gift. I hate that place.
Though you have a little girl or a bouncing baby boy this time, that doesn't mean you will the next time. So go neutral on the big stuff like carseats, strollers, pack ‘n’ plays, etc. Otherwise you will have to buy all new if you have a boy/girl next time or deal with the repercussions when your kid is 20...
Register for a few types of everything (strollers, carseats, etc). Then, come home and start reading the reviews on the web. VERY useful. Some seem great in the stores and then get HORRIBLE reviews. You will then have to take them off your registry. Since you already have a backup, no need to venture into hell, I mean BRU, again.
Ask other mommies what they loved/hated, used/didn’t use. Other moms are your greatest resource when you have questions about baby stuff. Though beware: some will say you HAVE to have a wipe warmer, other will say it is dumb (it is). Same goes with most things, just take it all in, then form your own opinions.
Don’t be tacky. Yes, you can register for your after-birth jumbo maxi pads and tummy-sucking-in-wrap, but don’t. Gross, girlfriend. Some things a mommy needs to keep private. Also, if you decide to breastfeed, get someone you know is going to buy you a big gift (like your mother or grandmother) to get you the breast pump you want without adding it to your registry. I think it is a bit gauche to remind everyone that peruses your registry that you will soon be milking yourself. Plus, it saves you the awkwardness of opening it as a gift from your co-workers at a co-ed work shower. Shivers.