1: Reverse around the corner - I tend to just reverse until I can see the bend of the corner of the road I am going into in my passenger rear window and passenger mirror, and then steer slowly/quickly depending on how sharp the bend is. The trick I think is to keep the car moving, the minute you slow down too much your car is going to go completely the wrong way. And you shouldn't really be more than the width of an A4 piece of paper away from the kirb. Once around the corner keep an eye on the middle of your back window and when it meets the kirb, quickly straighten your wheel and then go back however far you need to.
2: Reversing into a parking bay is all practice, depends on the car, your height etc. I reverse until the middle of my car/door column is aligned with the first line of the space next to the one I want to go into, and then quickly full lock.
I I I So I align my door column with the first 'I' whilst moving backwards and then full lock, and will go into the next space. Hope that makes sense! It's all practice, took me a while to find the right reference point that worked for me.
3: Parallel parking - park a doors width away from the car, slightly more forward. Reverse until the back of the parked car is in the middle of your passenger rear side window. 2 wheel turns to the left. Look in passenger mirror until the kirb disappears. Keep the car moving, slowing down here really messes it up. Full lock to the right until you look like you're going straight, glance forward to check you are, if you are and until you are then quickly straighten your wheel. If you are trying to squeeze in between two cars, then after the point when your kirb dissapears in the passenger wing mirror, switch to your wing mirror and wait for the whole of the car behind you to be visible in that mirror. Never had that method fail on me.
Apologies for the length, have to go into detail when explaining something 
practice makes perfect, try your manoeuvres whenever you get a chance and you'll soon find your own way of doing it.