Depends if it is your first time visiting an Ikea or not. If it is your first time, then I highly recommend seeing everything they have to offer, even when you know exactly what you want, unless you are pressed for time. I have found things that I did not know were offered by Ikea and now they are my go to store for those items. You should give yourself at least one hour to browse the show room floor, and another hour in the marketplace, with time to finish up warehouse. If you are there all day - plan to eat lunch or dinner there, the food isn't bad.
If you do not have hours to spend and know you need a coffee table in black with storage, then research online, call local store to see if it is in stock and just head to the warehouse to get it. If you need to see it before buying it, use the shortcuts in the store to get exactly where you need to go.
I enjoy going to Ikea, but I know I am spending a solid 3 hours there easy.