Kettlebell swings are awesome! And you can bet your ass that once I'm cleared to start working with weights again, I'll be HIIT training with some kettlebells like a fool.
There are a lot of articles out there already talking about proper form and things to avoid when doing swings. I recently attended a kettlebell seminar at a NSCA coaching clinic and want to add my two cents for cues and drills that made a lot of sense to me and I started using immediately afterwards.
First though, I'd like you to read the following article and watch the embedded video:
5 tips for a better kettlebell swing
What I see most often is what you see as the first example in the Good/Bad Swinger video. Squatting means your hips only minimally move front and back, mostly up and down, and that isn't going to produce the momentum on the bell you want.
1) Keep your shins vertical. Any squatting movement will cause your knees to move forward and mess up this vertical shin position. Think more like you're about to do a box squat or a Romanian deadlift, where you sit back and simply unlock your knees.
2) Don't let the kettlebell swing below the knees. I see this a lot, too. A person who gets the knees back cue suddenly starts letting that kettlebell pull her over and the bell just skims the ground. You control the bell, not the other way around.
3) Keep the kettlebell close to your naughty bits. In addition to not letting it pull you over, the closer the bell is to the fulcrum, in this case your hips, and this will be the most powerful place to fire the bell from for the next swing.
4) Pull the kettlebell back down from the top of the swing. Don't just rely on gravity to do the work, get your lats and abs involved and bring that sucker back down to your naughty bits!
Side Note: The seminar also went over the Turkish get-up, but with my shoulder being jacked, I wasn't able to participate in that one.