Here is what I think is important when wanting to get fit:
1. Decide to do it
Make a promise to yourself to start exercising. You do not want to fail yourself by breaking an important promise. Think positive - exercising will only do you good! Don't allow any "I don't want to..." - force yourself to get out and exercise, no matter what!
2. Find motivation
Look at pictures of your dream body, or health goal. Do you want to get fit, build muscles, and/or get healthier? Make a list of things you want to be able to do, and when you want to do it - but be realisitc! If you set your goals too high, your body will "shut down" and find your goals impossible to achieve.
3. Start slow
Don't push yourself too hard in the start. Start slow and listen to your body. Push yourself a bit, but not to the extent when you feel you're "going to die". What you want to think in the end of a the exercise is "I did it!", not "I couldn't do it".
4. Take a "day off"
Your body will need to heal after exercising, so take a day off during the week when you rest. If your muscles are sore from the exercise it's good to take a day off, although it's not harmful to workout anyway. But you might want to rest, and that's OK.
5. A bit longer and a bit harder
Slowly increase the distance or time you run/exercise. Increase the time with a few minutes every week, that's enough. Soon enough you will be able to feel how it gets easier and easier.
6. Use apps!
I use RunKeeper on my iPhone, which lets you know your speed, distance (through your GPS) and time you have been running. Today I used C25K (couch to 5 km), which I like! It has different programs for every week, and it tells you when to run, when to walk, how much time is left, and for how long you have been running. The only downside is you can't see how many kilometer you have been running. You can at least choose which week's program you want to start with, and you can re-do weeks if you want. I started with week 3, might do it again tomorrow, or start with week 4.
Food is fuel for your body, don't starve yourself! You can, however, go out for that run before breakfast. That way you burn more calories. Remember to eat a good breakfast afterwards though. And drink a lot of water - you will need it when you sweat more than you are used to!