Pack plenty of water. Even if you plan to hike for just a couple of hours, you do not want to run the risk of becoming dehydrated. Plan 1 L per person per hour of hiking.
Wear supportive, closed footwear and comfortable socks. Hiking boots are best. If you do not have boots, wear comfortable shoes with thick supportive soles. Make sure to take an extra pair of socks as well, particularly if you are going on a longer hike.
Wear comfortable clothes in layers that you can remove or add as needed. If you are hiking in an area where the weather is changeable, pack rain gear.
Wear a hat and sunscreen. Pack additional sunscreen.
f you are going somewhere with steep, rocky slopes, then fingerless gloves are a good thing to have on you. Normal work-gloves are good too. Hiking or walking sticks are also helpful for getting up a steep slopes, particularly if you carry a heavy pack or do not have good balance.