Stabilizing the counterpart sign

Stabilizing the counterpart sign (nimitta) isn't easy. Is there a 'technique' that leads to stabilize it? I.c. is there a 'technique' to develop/cultivate intensively the absorption factors (jhanangas)? With 'stabilizing' I mean: making the nimitta sharp, focused, completely free from tension (of the panca nivarana), so that absorption (1st jhana) can be attained.