Do as much walking in them as you can at the store. Walk around the store, if possible. See if there are any pinch points or places where the shoe rubs or is uncomfortable. Chances are, those places will keep rubbing, and will be miserable on a walk.
I have wide feet and narrow heels, so I have to look carefully for shoes that fit me well. I also want a really roomy toebox because my toes don't compress at all, so a narrower shoe just doesn't work for me.
I have to make sure the heels grip too, so they don't blister me. Everyone is different, so it's best to try on several pairs and different brands to find just the right fit. Otherwise, you won't feel like walking in them and will have wasted your money. Not a good feeling.