Want to go from the couch to running a 5K? Stop looking online and follow the tips below. They can help you run a perfect first race. (See also 8 Things I Wish I Knew Before I Ran My First Marathon.)
Use at least a 20-week training plan
Most online programs offer 16-week 5K training plans, but that's assuming you have a base to start from. If you're a true beginner (i.e., a couch potato) you will need at least 20 weeks. This will give you some extra time in case of a setback. (See Don't Choke on Race Day: Tips to Run a Better Race.)
When running on a treadmill, use a base incline of 2.0
This most closely simulates running outside. However, I suggest you start running outside exclusively. (Read Maximize Your Cardio Training With Intervals.)
For the first four weeks, run only twice a week
You need to ease into running. Pounding the pavement takes a toll on your entire body, especially your joints. You'll need plenty of rest and recovery if you are new to running.
Take a week off (when necessary)
If you ever feel injured, get cramps or suffer any joint pain, stop running. Rest, ice and don't be afraid to take a week off. If you're just uncomfortable, suck it up and keep running. That is the only way to get better.
Run for time
For the first eight weeks don't worry about speed or distance. If you are on a treadmill, cover the top with a towel and just look at the clock. This will help you establish a base. Then you can start following a training program. (Try this 5K training program.)