The proper hiking shoes are probably the single most important factor in determining whether or not you will enjoy your hike. It could be the most brilliant, sunny blue-sky day, but if your feet are burning from raw blisters on your heels, you'll be miserable. It is essential to choose the correct footwear for whatever type of hiking you plan to do. That said, the most important word to remember is: comfort.
Comfort is the single most important factor to consider when purchasing a new pair of hiking shoes. Along these lines, prepare to spend a good deal of time at the store trying out a variety of different styles of shoes. Bring the socks you plan to hike in to get the proper fit. Let a sales associate take a foot measurement and guide you to the correct size. Take your time and walk around the store. If the store has a small "terrain" area to test the boots out on, use it. If the shoe isn't comfortable, don't buy it, period. Don't assume it will break in and the little poke you feel at the heel will go away. If it's not comfortable now, it may never be so. Don't risk going home with a shoe that might sit in your closet because it causes you pain.
In addition to comfort, here are some key factors to take into consideration:
You can buy hiking shoes with low, medium, or high tops around the ankle. The higher the top, the more supported your ankle will be. A low top is fine for flatter terrain with few rocks. Consider purchasing a medium or high top if you hike more rugged terrain, over logs, rocks, and water. A higher top provides additional protection from low lying sticks, poisonous plants such as poison ivy, and insects.
If you plan to hike in a variety of weather and seasons, consider a waterproof boot. The waterproof boot should also be breathable, so that there is air circulating to your feet to help keep them cool. Waterproof hiking shoes are available at all price levels, although they do tend to cost a bit more than simply water resistant shoes. Water resistant shoes are fine for shorter hikes, and will still do a decent job of keeping your feet dry in mild weather or light rain.
The most common construction materials for hiking boots are canvas/nylon blends and leather. Leather tends to last longer and if well cared for, leather hiking boots can last for many years. Leather boots are also generally much heavier than their nylon counterparts. Nylon boots break in faster, and can often be worn right away for longer hikes. Leather boots tend to need time to get broken in by wearing them for shorter periods at first.
There are two different schools of thought in the hiking world regarding shoe weight. One is that you buy the lightest, most comfortable shoe you can. The reason for this is that if your feet are carrying the extra weight of heavy boots, they will sap needed energy from your body. Your legs will get tired quicker and put unneeded strain on your leg muscles. The other school says that your feet need all of the support and protection you can provide them. This school of thought maintains that you should buy thick-soled, heavy duty boots. These will provide maximum support for traveling over rugged terrain. They will stand up well to the elements, protecting your feet from a variety of weather conditions. It still comes down to comfort, but definitely take the weight of the shoe in mind as you test different styles.
Take a close look at the bottom of the shoe. Look at the tread pattern and how deep the grooves are. Compare a few shoes. The deeper the grooves, the longer the tread will last. Thinner treads will need to be replaced more quickly. Many higher end shoes can be re-soled, adding to the life of the boot. Ask the sales associate if this is the case for the boots you are considering.
Decide what's right for you in each category, and again, remember: comfort comes above all else