Well when defending your blinds you have several things to consider. Such as are you SB or BB, the position of the person raising and their image, and your cards.
You should be defending with marginal hands (and in general) a lot less from the SB than the BB. There is a chance BB resteals, and by defending your SB you will give BB odds
to call with worse hands.
The person raising and their position on the table matter greatly. EP raises usually are stronger than say cutoff or button raises. Also try to recognize what players attempt to steal the blinds the most and what hands they are showing down.
Lastly, your hand strength. You should only be defending with a small part of your range in the blinds. Generally try to defend with cards that will connect nicely with flops (suited connecters/one-gappers, pairs, paint cards). It will be much easier to continue in the hand oop with these hands.