These days you’ll be asked for loglines all the time. It’s a great exercise to undertake, as you have to reach into the soul of your work to create a decent logline, and it’s a way to X-ray your story. (Please check On Blake Snyder’s SAVE THE CAT: loglines)
Want more about this subject? Two great articles follow where you’ll find all you need to know about loglines:
From Indiewire, How to Write the Perfect Logline And Why It’s As Important As Your Screenplay, and from Raindance, 10 Tips For Writing Loglines. Read them carefully and practice. Let’s face it, nowadays a proper screenwriter needs to master this particular craft.