Take small steps such as:
- Trade your scented candles or oils for fresh flowers.
- Skip the household aerosol sprays.
- Quit smoking right away, and don't allow anyone to smoke around you.
- Paint Fumes
- Tobacco Smoke
- Improperly Maintained Stoves
- Kerosene Heaters
For more Breathe Easy tips, read this article at Eco-Pregnancy and this one.