When someone asks a how question, the easiest way to answer is with the preposition by + a gerund.
How can I stay in shape? You can do it ______________________________
- by walking places instead of driving.
- by eating healthy food.
- by going to the gym. To make your answer negative, just but the word NOT in front of the gerund:
You can stay in shape by NOT being a couch potato.
Let’s try another example: How can I be an interesting conversation partner?