One tip I was given several years ago, at one of Joanne Mallon's workshops that I've never forgotten, was "If a journalist contacts you respond immediately".
Journalists are nearly always working to tight deadlines (maybe they could use some time management!) - they need something submitted within a few hours or a couple of days if you're lucky, so be ready to respond. If they leave you a message or send you an email - get back to them as soon as you can or they'll have moved on to the next available person and your opportunity will have been lost.
Magazines are often planning what goes into print two or three months in advance, so you many be responding in the Summer to something that goes in to the Winter editions. I've recently submitted an article which won't be out until December, even though the deadline was two weeks ago. Newspapers often print more quickly - especially if they're looking for comment on current news.
I get called every couple of months and I'll always call them straight back or if they email me and there's a contact number, I'll call them rather than just reply by email. It's resulted in many of my articles being published in national publications. Not all of them always make it - copy changes and articles get dropped but the opportunity is there if you take it.