What you are facing is a problem with the basics.
Ask yourself, what affects DOF?
Focal length, focus distance, bkgnd distance, aperture
Less DOF - longer FL, near focus distance, further bkgnd distance, larger aperture.
If you are constrained by some of those parameters, you will have to play with the others to get that shallow DOF.
As for how you should shoot (head shots, full body, etc), its entirely up to you as the photographer.
And also knowing what your equipment can give you.
Shoot more and be more conscious of what/how you shoot and what your equipment can do.
You will get there for sure