Wearing old running shoes or wearing the wrong type of running shoes for your foot and running style can lead to running injuries.
Go to a running specialty shop, where knowledgeable salespeople can evaluate your running style and foot type. They will recommend you a suitable shoe after determining whether you're an overpronator, underpronator, or neutral runner.
Once you get the right pair of running shoes, make sure you replace them every 300-350 miles because the loss of cushioning can lead to injuries. About halfway through the life of your shoes, you might want to buy another pair to rotate into your runs. Your shoes will last longer when you allow them to decompress and dry out between workouts. Also, having a fresh pair of shoes as a reference will help you notice when your old ones are ready to be replaced.

Many runners, especially people who are new to running, make the "terrible too's" mistake. They get so excited and enthused about their running that they do too much mileage, too fast, too soon. They mistakenly think that "more is better" when it comes to running. As a result, they often start to develop common overuse running injuries, such as shin splints, runner's knee , or ITB Syndrome.
Be more conservative than you think you need to be with how often, how long, and how much you run, especially early on in your development. Increase your mileage gradually. Don't let your weekly mileage increase by more than 10%. If you're new to running or are coming off a long break, start with walking first, and then progress into a run/walk program.
Pay attention to aches and pains. If a pain gets worse as you continue runs, that's a warning sign that you should stop your run. Listen to your body for injury warning signs and know when you should not run through pain.
Take at least one complete day off from exercise each and every week. Don't ignore rest days -- they're important to your recovery and injury prevention efforts. Your muscles build and repair themselves during your rest days. So if you run every day, you're not going to gain much strength and you're increasing your risk of injury.

One of the most common injury-causing running form mistakes is over striding i.e. landing heel first with your foot well ahead of your body's centre of gravity. Some runners assume that a longer stride will improve their speed or running efficiency, but that's not the case. Over striding wastes energy since it means you're braking with each foot strike
Make sure that you don't lunge forward with your feet. This is especially important when running downhill. Focus on landing mid-sole, with your foot directly underneath your body with every step. A short, low arm swing is the key to keeping your stride short and close to the ground.

Some runners swing their arms side-to-side, which makes you more likely to slouch and not breathe as efficiently. Some beginners have a tendency to hold their hands way up by their chest, especially as they get tired. You'll actually get more tired by holding your arms that way and you'll start to feel tightness and tension in your shoulders and neck.
Try to keep your hands at waist level, right about where they might lightly brush your hip. Your arms should be at a 90 degree angle, with your elbows at your sides. Imagine a vertical line splitting your body in half -- your hands should not cross it. Keep your posture straight and erect. Your head should be up, your back straight, and shoulders level. When you're tired at the end of your run, it's common to slump over a little, which can lead to neck, shoulder, and lower-back pain. When you feel yourself slouching, poke your chest out.

Some runners wear the wrong type or too much or too little clothing for the weather conditions, leaving them uncomfortable and at risk for heat-related or cold weather-related illnesses. .
Wearing the right type of fabrics is essential. Runners should stick to technical fabrics such as Dry Fit, Thinsulate, Thermax, CoolMax, polypropylene, or silk. This will wick the sweat away from your body, keeping you dry. It's very important to make sure you don't wear cotton for this layer because once it gets wet, you'll stay wet, which can be uncomfortable in warmer weather and dangerous in cold weather. In the winter, make sure that you don't overdress. You should add 15-20 degrees F to the temperature when determining what clothing you should wear -- that's how much you'll warm up once you start running. In the warmer weather, stick to loose, light-colored clothes.

Some runners who are training for specific races or certain goals run too hard, run too many miles, and don't allow for proper recovery time. They assume that running every day will help them get fitter and faster. Overtraining is the leading cause of injury and burnout for runners.
Here are some ways to avoid overtraining:-
Increase your mileage gradually. Don't let your weekly mileage increase by more than 10%.
Try to give yourself periodic "rest weeks" by dropping your mileage by 50% every fourth week.
After a hard run, take a day off. Rest days are important for your recovery and performance
Add some cross-training activities to your schedule. Doing activities other than running prevents boredom, works different muscles, and can give your running muscles and joints a break

When it comes to running long distance races, one of the biggest rookie mistakes is going out too fast in the beginning of the race. Most runners have at least one story about a race when they felt so great during the first few miles that they ran ahead of pace, only to crash and burn during the final miles.
Here are some ways that you can avoid going out too fast:-
The best way to avoid the temptation of going out too fast is deliberately run your first mile slower than you plan to run the final one. It's tough to do, since you'll most likely feel really strong in the beginning. But keep in mind that for every second you go out too fast in the first half of your race, you'll lose double that amount of time in the second half of your race.
Try to make sure you're in the correct starting position. Don't start yourself with faster runners because you'll most likely try to keep up with them. Start your race at a comfortable pace and make sure you check your watch at the first mile marker. If you're ahead of your anticipated pace, slow down. It's not too late to make pace corrections after just one mile.

Many beginning runners underestimate the importance of nutrition, for both their running performance and their overall health. What and when you eat before, during, and after your runs has a huge effect on your performance and recovery.

Try to eat a light snack or meal about 1 1/2 to 2 hours before a run. Choose something high in carbohydrates and lower in fat, fibre, and protein. Some examples of good pre-workout fuel include: a bagel with peanut butter; a banana and an energy bar; or a bowl of cold cereal with a cup of milk. To avoid gastrointestinal distress, stay away from rich, high-fibre, and high-fat foods.
If you're running more than 90 minutes, you need to replace some of the calories you're burning. You can get carbs on the run through sports drinks or solid foods they are easily digested, such as as energy-gels, bars, and even sports jelly beans designed for long-distance runners. A basic rule of thumb is that you should be taking in about 100 calories after about an hour of running and then another 100 calories every 40-45 minutes after that.
Replenish energy as quickly as possible after a workout. Studies have shown that muscles are most receptive to rebuilding glycogen (stored glucose) stores within the first 30 minutes after exercise. If you eat soon after your workout, you can minimize muscle stiffness and soreness. You'll want to consume primarily carbs, but don't ignore protein. A good rule of thumb for post-workout food is a ratio of 1 gram of protein to 3 grams of carbs. A peanut butter and jelly sandwich, a fruit and yogurt smoothie, and chocolate milk are examples of good post-run snacks.
Don't follow a low-carb diet when training. You need a certain amount of carbohydrates in your diet because they're a runner's most important source of fuel.

Many runners underestimate how much fluid they lose during runs and don't drink enough while they're running and after they're finished. As a result, they suffer from dehydration, which can be detrimental to their performance and dangerous to their health.
Runners need to pay attention to what and how much they're drinking before, during and after exercise. Even if the weather is cold, you still need t make sure you stay hydrated. Here are some simple rules for drinking and running:
An hour before you start your run, try to drink 16 to 24 ounces of water or other non-caffeinated fluid. Stop drinking at that point, so you can prevent having to stop to go to the bathroom during your run. To make sure you're hydrated before you start running, you can drink another 4 to 8 ounces right before you start.
You should take in 6 to 8 ounces of fluid every 20 minutes during your runs. During longer workouts (90 minutes or more), some of your fluid intake should include a sports drink (like Gatorade) to replace lost sodium and other minerals (electrolytes).
Don't forget to rehydrate with water or a sports drink after your run. You should drink 20 to 24 fl oz. of water for every pound lost. If your urine is dark yellow after your run, you need to keep rehydrating. It should be a light lemonade colour.