Here's a simple but tough workout to get you prepped for fall 5k season. The advanced version starts with a mile run. Modify based on your fitness level and experience. New runners may want to start with just a quick run around the block.
Run 1 mile
Rest half as long as it took you to run.
Repeat for 3 runs.
Push yourself! Try to hit the same pace every run. This takes as much mental toughness as it does physical. Get strong. Get quick.