Bike and Gears
If you are starting off from scratch, you need to think of buying a bike first before anything else. I said "think" because not all bikes are the same.
When buying your first mountain bike, you have to identify the type of riding you will be doing most of the time as bikes are designed for specific style and terrain. To make matters simple, I suggest that you get an all-terrain hard tail mountain bike to start with (but you are free to choose from other types of bike depending on the riding surface you want to ride).
Then, there are gears. It's a no-brainer that you must have a helmet whenever you go out for a ride. Not only because it protects your head from any possible injury you may sustain during a crash, but also because it is prohibited to ride without wearing one.
Consider buying at least 3 pairs of gloves so while you are wearing one pair, the other pair goes to the laundry while the third pair goes to your backpack as a reserve. Mountain biking shoes are great for comfort and good grip on the pedal. Sunglasses regulate and enhance the light and serve as a protection from harmful rays and other elements that can enter your eyes such as dust, small rocks and insects.
Tools
Every biker experiences getting flat and mechanical damage. Get a good set of tire repair kit including mini pump, patches, extra inner tube and glue. A multi-tool that includes wrenches will allow you to repair any mechanical damage of your bike. Broken chains can be a big problem while on the trail. Make sure to include chain tool in your arsenal.
Location. Location. Location.
Common conception is that mountain bikes can only be used on unpaved surfaces. The truth is you can use your mountain bike no matter where you are. So whether you are stuck in the city that offers everything other than nature or you have an access on a local bike or a mountain trail, you are good to ride.
Riding companion
There is nothing wrong with riding alone but you really have to consider joining a group of riders especially if you are planning to ride on remote places where there are no people around. A riding companion will come in handy in case you need medical assistance or simply experience a mechanical breakdown while on the trail. Also, experienced riders are good sources of valuable information on the best places to ride and how to ride safely and properly.
Safety Concerns
While mountain biking is a relatively safe sport, taking proper precautions are necessary. Aside from wearing a helmet and gloves, consider wearing padded shorts, elbow and knee pads. Keep your speed in check. Do not ride beyond your capabilities. Do not ride if you are uncomfortable with the terrain. Keep your physical fitness high. Take it slow; do not spend your energy on the first kilometer of the trail.
And most importantly, keep your energy high by drinking fluids and eating right before and during the ride.
