The biggest mistake you can make when you start running is being overly enthusiastic. It is likely you have not run properly since school, and as mentally prepared as you might be to get going, you probably are not physically ready. Body conditioning is a good way to ease yourself in; cross-training leading on to easy runs is better than going from zero to flat out.
Keep it comfortable. A lot of people think they need to really push themselves to get better, but this can have the opposite effect. If you go for a fun 20- to 30-minute jog, you are more likely to be motivated to go again than if you end an hour-long run with a sprint finish, in pain and heaving like a donkey. Some people feel embarrassed if they have to stop running and start walking, but what is important is feeling comfortable. The joy of running often comes from being in a park or in the countryside, so let yourself run for a bit, slow down and appreciate your surroundings, then start again. Don’t think about how far you are going to go – just enjoy the journey.
Make sure you get shoes that properly support you, so you don’t hurt yourself. And try to stick to softer surfaces such as grass. Running on concrete in the wrong shoes can end in disaster.
If you feel intimidated by running long distances, it can be beneficial to start on a treadmill. However, the goal should be to run outside, because it is far more enjoyable.