Attempting a back somersault without learning the above trampoline tricks will almost certainly result in an accident. As long as you have mastered these moves, particularly the back drop, then you will be surprised how easy the back flip is. In fact it is easier that a front flip as you are able to judge your landing. The real problem with learning a back flip is the 'fear' of going backwards.
THE ROLLOVER
Start by simply doing a backward roll on the trampoline, keeping your body tucked up tight. Progress to a back drop, lifting your hips and getting your legs over your head, landing on your hands and knees. You must now try to do this same move, but right in the middle of the trampoline. Perform the Back drop and Really lift your hips up. This is how you stay in the middle of the trampoline. The idea is to be able to perform this move to your feet. This is a back-rollover the feet.
THE TUCK JUMP
Before going on to the next stage, you need to practice the tuck jump. You should have a good high jump, bringing your knees in tight to your chest and then open out.
The back flip is simply a tuck jump, lifting the hips and tilting backwards. This motion of lifting the hips and tucking tight creates the rotation needed to complete the back somersault. As you go over, you can see the trampoline bed and will be able to judge your landing.
BACK DROP HIP LIFT
The importance if the HIP LIFT can not be emphasized enough. To practice this move, you should place a gym mat, or toddler size mattress, or a piece of foam 4 inches thick on the trampoline. Jump on the mat, in the middle and do a back drop, really exaggerating the lift of the hips. You may land a little higher up on your back, hence the need for the softer landing.
The feeling should be that you are lifting your hips above your head. Once you have lifted the hips up, a sharp tuck will do the rest for you. However, getting over the 'fear' is the hard part.
GETTING OVER THE FEAR
First, remind yourself that if you Lift the Hips and Tuck Tight, it is very unlikely you will do anything other than perform a backflip. If you 'chicken out', then it is likely you are going to land on your head. Be Determined.
Next, ask a friend to stand on the trampoline, balancing on the frame, next to you. (Their feet must not be on the trampoline bed as it will kill your bounce). With your friend standing close by, you must bounce just a few times (maximum 5 bounces), take off lifting the hips, tuck up tight at the top of the bounce and get your hips over your head. The rest is just about done for you... you will land.
It helps to get your friend to 'count in', otherwise you keep bouncing and 'thinking', rather than Doing! They can count one... two.... three... TUCK, with the word Tuck being shouted. This creates urgency and can help you tuck up tighter.
ADDITIONAL TIPS
It is a myth that you need 'room' to do a back flip. You should NEVER take off at one end of the trampoline, 'giving you room' to perform the back flip. ONLY EVER TAKE OFF IN THE MIDDLE
If you are 'twisting' during the back flip, this is due to your fear and you are trying to compensate by twisting to see the trampoline beneath you. Go back to the Back rollover the overcome this.