Only a few pointers.
Practice, practice, practice, that's what I recommend. Like Johnny pointed out heaps of videos on the net of how to counter steer a bike. It also depends on the bike you have and the components on how well you rail corners, some bike geometries are a lot harder to get them to turn in at different speeds. Watch a few videos and pro riders, go out and see what works for you.
Body position on a bike will change through out a corner and depending on speed, how loose the trail is, how high the berm is, how tight the corner is. You will figure this out with experience and practice. The turning your hips helps you steer the bike and look through the corner, your bike normally follows where you look. Your outside knee should be turned touching your frame or almost touching, that position will also help lean your bike and not your body into the corner. As you start coming into the corner you should start turning your hips, as you get to the centre they should be at the most angle require for that corner, as you come out of the corner you need to start straightening up.
Tyre choice, pressures on the front can make a big deal and running a lower seat post height, hence dropper posts are good for cornering.
The biggest trick I found with cornering hard after body position to countersteer was being really smooth with your turning and weight distribution through out the corner. If you are too aggressive you will slide the front or rear tyre and loose all your speed if not come off the bike.
I also push down on the front bars a bit with minimal weight, when I'm on really loose surfaces. I found that on bikes with really slack HA and long travel forks it helps a bit. Some bikes will be weighted to corner well with Geo and some bikes will just be hard work, take into account things like high or low bottom brackets heights and seat post angles.