For quick and dirty tips that are always interesting and relevant, check out Grammar Girl!
Grammar Girl is quirky and fun, and my students love listening to her lessons on grammar (much more than they like my own!). She gives enough information that the students can build schema and have some context for WHY a particular rule is what it is. The examples she uses are accessible and often quite funny.
How I Use It
I paste links into students' Google Docs as they are writing to provide a mini-lesson on a recurring error. Students get a chance to learn as they write, and I don't have to correct their mistakes after it's too late. Sometimes, if I see a particular error over and over again, I'll assign a lesson for homework. Some of my students have even subscribed to her weekly podcast.