I came across Tim Squirrel's YouTube channel about 5 months ago. Tim is a PhD student in Edinburgh. Like me, he does some teaching and marking. Unlike me, he's fantastically sensitive to the specific problems that undergraduates have when writing essays.
His advice is sensible, funny and not buried in the depths of an academic book. He's featured in The Guardian and is my go to source for preparing sessions on essay writing. I completely agree with his position on Wikipedia (use it, don't cite it).
If you're not a fan of YouTube videos, Tim has a blog called 'How to write better undergraduate essays' that outlines his essay writing approach in detail. I suggest you all check it out.