1) First of all cut off frequency value should be decided and it remains constant.
2) (1/wcr) value should be constant if it is an RC filter and R & C should be choosen according to relevence to cut of frequency.
3)For high pass filter, transfer function numerator will carry the highest power of s and for low pass filter denominator will carry the highest power of s.
4) In case of band pass or band stop,any intermediate power of s will appear in the numerator of transfer function.