Decide why you need boots. Camping with a backpack, hiking with a light bag and traveling internationally all call for different kinds of shoes. Put on a pair of the socks in which you intend to hike. Go to a shoe store, the shoe department of a store that sells recreational equipment, or best of all, a specialized outdoor retailer. Find the lightest boots suitable for the kind of walking you plan to do.
Leather is best for all purposes.
Boots with inflexible soles are best for long walks with heavy bags. Lighter boots or heavy walking shoes are better for most other applications. Try on the boots, tie them as you are likely to on the trail, and knock at the floor with your toe. If your foot slips appreciably, you are likely to get blisters. Ask for a smaller size, or try a different model.