You can train your computer to better understand you using the local speech recognizer built into Windows
- Open Windows Start
- Type Speech Recognition
- Click the first result
- Click on Train your computer to better understand you.
- Follow the guide and speak into your microphone.
This will make the recognizer know how you sound and will be able to better distinguish your voice from noise from eg. steering wheel or other people nearby.
Do this training at least twice! Also over time, the recognition gets better as it learns as you talk to it.