Modifying the walk to challenge our balance systems can be done by taking a few minutes during the walk to stand or walk in tandem, or stop for a minute and stand on one foot, but always think of safety and have something to hold on to.
Limbering up the entire body including the feet can be helpful before a walk especially if you have arthritic feet. Again have something to hold on to, lift one foot, point and flex it, circle it, wiggle your toes inside your shoes.
For example, if your Fitness level allows, you can walk more briskly, and maybe add some incline if it's available, if your goal is to lose weight or make large gains in your cardiorespiratory Fitness. If you happen to get winded, slow down a bit until you recover. Remember you should always have clearance from your doctor before you start any exercise program.