Shoe shop after work: Our feet swell in the afternoon so go hit up your favorite store in the late afternoon because a shoe that feels great in the morning may feel tight later in the day.
Short is good: Shorter, wider heels will provide more stability and support. Look for a 1.5 inch heel if you're going to wear them often.
Vary it up: Don't wear the same heels every day. If you use variety your feet won't get used to being in the same position and it will lessen the chance of shortening your Achilles tendon.
Stop Punishing Your Feet
Give them a break: Switch to some sensible flats when you can so your feet can rest. This especially goes for driving because you have less control with heels.
Save them for special occasions: For those hot heels (you know the ones), wear them sparingly, like for evenings out or parties. And sorry but you will have sore feet from these -- skinny 5-inch heels do you no favors.