there are essentially five major classes of techniques used to subdue your opponent: strikes
, pressure points
and joint manipulations
The human body only bends in certain ways -- elbows only bend this way, shoulders only turn like that.
This knowledge can be used to not only successfully apply a known technique (such as a reclining arm-bar), but to improvise should an opening appear.
Joint manipulation is very important to keep in mind when grappling a large opponent -- they may have a big, thick neck but their shoulders still only twist so far before they dislocate.
An opponent with joint hypermobility (aka double jointedness) isn't a concern -- a correctly-applied technique will work just as well.