I wanted to share a recommendation of my own - a tried and test one. Ages ago I got a copy of Writing for Magazines by Diana Cambridge and was impressed by its simplicity, layout and straightforward tips. I read it cover to cover and decided to work from the letter writing section. I emailed my letter (my first) to Psychologies Magazine over a month ago and forgot all about it. I'd heard nothing back but I was writing again so I was happy with the outcome.
Then I spotted this yesterday whilst casually flicking through the magazine during a quick lunch break:
Not bad for a first go. This wasn't a paying gig but then if I wrote for the money I'd have given up a long time ago!