Quite a broad question. Agencies and publicists that are experienced have learnt many things over the years, which will all play part of best practice. As a staring point, would suggest you think about the following:

- Ensure your pitch is concise and to the point. Lead with what is most newsworthy to readers of the publication you are targeting
- Be harsh. Consider if what you are sending them really news?
- Rearsearch the journalist and tailor pitch to reference articles they have written or areas they have an interest in
- Go to the right person. Don't sent an irrelevant story to the journalist. Make sure they actually write about what you are sending them
- Be prepared. Have facts and information ready
- Use the phone. Imagine how many emails they get each day! You're far better pitching on the phone, and talking over the news and then following up with tailored into based on their feedback

If you get the approach wrong then your pitch is going to be sent to the junk folder and you simply won't get a reply or answer.

Hope that's not too blunt! Hope it helps. Thanks.