Your shoes make a HUGE difference, and the wrong choice can make your hike/run miserable or even dangerous. For longer excursions, or in locations that feature steep hills, gravelly, rocky, or slippery terrain; regular tennis or street shoes won't do. Be sure to purchase good quality hiking or trail running shoes that will keep your feet comfortable and protected and provide the traction needed for any conditions. Choose shoes with a good, supportive fit and excellent comfort. If the shoes are pinching your feet in the store, just imagine what that will feel like after 2 or 3 hours! Also, pay attention to the heel cup- is it secure or does your heel slide around a bit when you walk? (a loose heel cup is sure to give you some nice blisters on the back of your heel) Do you have special issues to consider such as plantar fascitis or overpronation? If you are unsure of where to look for a good pair of shoes, visit a specialty store such as Fleet Feet or REI where there are trained associates to assist you in finding the right shoe. Good shoes don't necessarilly have to be expensive, but you should be prepared to invest in the best that your budget can afford.
Socks are also something that should receive thoughtful consideration- the wrong socks can ruin a good hike or trail run! Special hiking socks can be purchased at specialty and sporting goods stores. Socks should not be abrasive and should manage moisture well so that your feet aren't super sweaty and sliding around inside your shoes. They should also be the appropriate thickness for your shoes.
Sometimes even with great socks and shoes blisters or sore spots may occur. Having a supply of bandaids, moleskin and bunion cushions will help solve these issues. Moleskin & bunion cushions can be used preventatively to avoid painful feet (they stick onto the skin and cushion the area receiving too much pressure or abrasion) You can purchase moleskin & bunion cushions at any Walgreens, Target, and most other similar stores.