Decap Tactics
1.Tug
Most beginners use this strategy as it is easy to execute. Simply grab on to your opponent's head and hope to rip his head off. It is not very effective.
Expansion
You can execute this tactic by grabbing your opponent's neck then letting go. When you let go your hand will expand and pop his head off.
Guillotine
The most effective tactic by far. You must get your arm behind his head at least elbow deep then you contract your arm and wrist which will hit the back of his neck so hard and fast that it'll chop it off and send it flying.
Slam
Must we explain this? Slam his head really hard on the ground and hope it gets decapped.
Dismemberment Tactics
Many of the decap tactics may also be utilized to dismember your opponent such as Expansion, Slamming, Tugging & the Guillotine but here's some additional ways to dismember your opponent.
Clinch
Try to grab your opponent that get a power strike on him. Since your grabbing him rather than getting pushed away by the power strike and absorbing some of the momentum of the strike he will stay in place and take the full damage of the might blow.
Swipe
Most commonly used in the opening frames. Your opponents arms will most likely be spread out and exposed therefore giving you the opportunity to grab it so fast it comes off. You should utilize your elbow, chest & wrist to increase your chances of dismembering him.
Fracture Tactics
Just use all the tactics above but with less force so that it only fractures rather than getting ripped off.
Grab
Try to grab their hand to manipulate it into self grabbing.
Slick Trick
Pretend your using a decap opener so that they try to block it then move your arm backwards so they self grab.
Damage Point Tactics
Just use all the tactics above but with way less force so you just get damage points instead of ripping it off or fracturing it.

Fracture- almost all the times i have seen a frac it was due to a you grabbing thier hand and them self grabbing. Hope this helped