Vilhjalmur Stefansson, an Icelandic polar explorer, is quoted as saying, "An adventure is a sign of incompetence" [source: Layman]. Experienced hikers know that poor planning and carelessness can ruin your day. An "adventure" in the rugged Sierras can easily turn into a life-threatening disaster.
The first rule is to know yourself. Hikes here can be very strenuous and may take you to high altitudes. Overexertion is one of the most common difficulties hikers encounter. Understand your limits. You may need to spend a few days acclimating to the altitude before you go on a big hike. Take breaks and don't overdo it.
Also, remember to drink enough water. Dehydration from heavy exercise is a common problem. Carry water for short hikes, and bring a filter for longer stays. Drinking unfiltered water from streams and lakes invites some unpleasant diseases.
There's safety in numbers, so hike with a partner or small group. Leave word as to where you're going and when you'll be back. Take a cell phone with you, but don't depend on it. There may be no reception in the backcountry.
Even for a day hike, learn something about the terrain, the elevation gain and availability of water on the trail you'll be tackling before you head out. Keep an eye on the weather, too. Thunderstorms sweep through the Sierras regularly during summer. Carry rain gear or a tarp -- getting soaked can reduce your body heat to dangerously low levels. Lightning may be a problem, as well, especially at higher elevations. Take precautions during severe storms: Lie down and avoid exposed areas.
The right gear can help make for a safer, more enjoyable hike. Good shoes, well broken-in, are essential. Make sure you have a warm jacket, even during the summer, as high-country weather is unpredictable. Take a supply of food, especially energy bars and nuts, which are convenient and rich in calories (you'll be burning a lot of them). Also, don't forget a first aid kit and sunscreen. Additionally, walking sticks can save you from a sprained ankle on rough terrain, and a GPS device or compass and topographical map are essentials to avoid getting lost.
It all comes down to common sense. With adequate preparation and some basic precautions, the Sierras will reward you with a hiking experience you'll remember for the rest of your life. "Going to the mountains is going home," John Muir wrote. "That wildness is a necessity" [source: NPS/Backpacking].