How to email journalists without wasting their time

Apart from the points that you mentioned in your posts, that are commendable and actionable, one should try to get into radar of the journalist by following him on Twitter and replying to his latest tweets.

What I think is as App development takes time, therefore, meanwhile one is developing his app, he/she should make a list of potential journalist that he/she is going to send email later.

After making that list, consider following them on Twitter, reply to their tweets for quiet some time and then if you will send email to them, your odds of getting through increases.