Stick with the most important ones all the time. Don't fall out of communications with them and then expect them to positively react to a story the next time you call. Always send thank you notes after every story is written no matter how big or small. Do things that other PR people overlook. Make yourself unique.
Press releases are very important.
Unfortunately, most are written too commercially. Tell the whole story. See what their reactions are and then go back and do a rewrite to cover the points that they zero in on. Unless you have major breaking news, there are many angles to a story. The press can be very helpful in shaping the lead of a story, and in helping you ensure you have all of the backup you need to score headline news.