Rule 1 : RESEARCH. Figure out what sort of thing you want, take measurements for the space it has to fit BEFORE you go. Ideally - already sign up to the Ikea website and build yourself a shopping list that includes all the different options you MIGHT want to buy, and then print it out citing the store you're going to visit - as it will then list stock numbers AND the locations of all the various part you might want to get.
Bad advice. Not the measuring part, that's dead on, but the shopping list with locations.
The problem is that the catalog and website pictures don't really give you a good idea of what the stuff actually looks and feels like. I know I looked at a couch on their site and had decided what I wanted, what material, etc.. before going and when I got there, I got a totally different couch. The one I picked from the website felt cheap, the material color was nothing like the picture and it was uncomfortable to boot.
The Ikea experience is all about being there and seeing the stuff. Don't cut straight to where you're going, take the time to shop around and look at all the stuff they have to offer.
OP : do yourself a favor, just go walk around a bit, see the stuff you like, take the free pamphlets with all the dimensions and kit possibilities, then go back home, measure stuff out, build out your kits on paper and go back the next day to purchase your stuff.
Plus with my way, you get to eat the Swedish meatballs twice.