Hi! Kedar:
What I've done and worked for me is: first of all, identify internal auditors that really like to be an auditor.. those that the supervisor is telling them (forcing them) to be auditors, they will not be highly motivated to conduct audits.... however, I never make a distinction of a "good" or "best" auditor.. what I've been doing is to recognize the effort of all of them, with their supervisors, in open meetings and also, providing certificates to them for different "refresher" trainings.....(those of one-two hours meetings talking about the changes of a standard or customer requirement).... also a good lunch after the "external" audit...(good lunch for them could be even a pizza or a hamburger... it does not have to be something fancy)...
I invite them also to participate in the external audits, as observers and to help me out during the external audit "to shadow"/escort the external auditors... it works pretty good... they learn more and become more interested in audits and how to conduct their own internal audits.
Also, when the economy/budget allows it.. I give them T-shirts, pens, or even nice folders to keep their auditor notes... sometimes, a "congratulations" note/card (or verbal) helps a lot!!
greetings,
Soulma