1. A good pair of hiking boots is invaluable. Many places have unexpectedly rough terrain. Even if you're out for a moderate level hike, you don't want to slip on a rock or twist your ankle because you were wearing flimsy sneakers. It's well worth the investment. Break in the boots before you actually go on a serious hike.
2. To decrease the chance of getting blisters, I have found that foot liners are useful. These are typically thin, white "socks" which you put on first, before the real sock. They protect your foot from rubbing against the outer sock.
3. For the real sock, wear something that is wool-based. These are often labeled as "hiking socks" in sports stores. Wool won't hold in the sweat as much as those white cotton socks and will allow your feet to breath. Sweat accumulation in socks is a cause of blistering, because a wet sock tends to rub against the skin more tightly than a dry one, which slides along.
4. Water bottles and a water bottle holder to wear on your side are also a necessity. A good climb of a moderate level peak like Monadnock can dehydrate you very quickly, especially in the summer, and you don't want your thirst to affect your enjoyment of the surroundings or your ability to climb effectively. At least two quarts of water is a good idea for a climb like Monadnock, which is about 3200 feet elevation and about 2 miles of hiking trails to get to the top. It doesn't sound like much, but it's an uphill climb that can dehydrate you quickly.
5. A soft backpack (for day hikes) with several compartments to store items is essential. Bring along items such as bandaids, antiseptic ointment, mole skin to cover blisters (either when they start or, preferably, before they start if you are blister-prone), large bandaids for the same purpose, flashlight (in case you get lost and end up hiking in the dark), outerwear such as a wind breaker and pants, bug spray, sun block, camera, binoculars, compass, map, cell phone (take down the number of the park's staff office ahead of time).
6. Let someone know where you are going. If you get lost and don't return, someone will know enough to alert the park staff.
7. A cell phone is not a replacement for common sense and for preparation as outlined above. Also, depending upon where you are hiking, a cell phone may not work!
8. Take frequent rests as needed. Go slowly on
your way downhill, since this is when most injuries occur.
Gravity is pulling you down, and you are tired, so you tend to slip on
rocks and lose your footing more easily.
Grand Canyon and Havasu Canyon