Planning exercise is very important. The first thing you need to do is decide at what level you want to start. This depends on several factors like age, gender, current level of fitness, weight, pre-existing injuries or medical conditions and time. If your over weight and have a heart condition it is not sensible to start running 10k every day. Everyone is different and there is no such thing as a routine that works for everyone.
Warm Up
Prepare your body for exercise, don't go all out straight away as this will be a shock to your body, start with some slow low intensity exercise to prepare your muscles and joints for your routine. This gradual warm up will prepare you mentally for exercise, its a lot harder to exercise if your mind set it that exercise is hard and painful every time your start.
Stretch
Use safe stretches to improve your range of movement and prevent post exercise soreness.
Use the correct equipment
If running its important to wear the correct type of running shoes to reduce pressure on joints and muscle, this will help avoid injury. Using the correct equipment is important in all forms of exercise.
Use good technique
Its is very important to use good technique with smooth movements; good balance; regular and relaxed breathing; body alignment and good posture. Good technique will see you get the most benefit from exercise and will help avoid injuries and post muscle soreness.
Don't over do it in your first session
If you have never exercised before or have not exercised for a long period of time it is very important not to over train in the first few sessions you undertake. It will be a shock for your body the first time you exercise. It takes your body time to adapt to the new stress you are putting on it. If you over train at the start your will get sever muscle soreness and a high risk of injury. Along with this it will deter you from further exercise mentally as well as requiring long periods of time in between exercise for your body to recover.
Cool down
After exercise your body need to adapt from its active state back to its non active state. Doing a light cool down routine after you have exercised will prevent injury and muscle soreness post exercise
The following are some of the stretches I would recommend doing before going running, they focus mainly on the lower body. You can find a full range of stretches on this website: http://www.stretching.name/index.php?filt=all [1] all the following pictures came from http://www.stretching.name/ [2] and are licensed under the creative commons share a like licence.
Links
[1] http://www.stretching.name/index.php?filt=all
[2] http://www.stretching.name/
[3] http://www.stretching.name/index.php?filt=legs&num=1
[4] http://www.stretching.name/index.php?filt=legs&num=26
[5] http://www.stretching.name/index.php?filt=legs&num=11
[6] http://www.stretching.name/index.php?filt=legs&num=2
[7] http://theingots.org/community/node/14013