Keep your head up and relax your shoulders. If it is getting hard to talk or catch your breath, just slow down a bit. Start with three sessions per week and work up to five days a week. Add 5 minutes to each workout as your fitness improves. Stretch the major muscles at the end of each walk, particularly the calves and hamstrings.
Music can be really fun to listen to, particularly on a long walk.
For safety reasons, keep the volume low enough to hear traffic and other noises around you. Find a walking buddy - nothing helps more with motivation. Keep a log of your progress so you can look back at it and feel accomplished. Drink plenty of water. Wear a billed hat, sunglasses and sunscreen.