How to make an offer on a property that's been sitting for 80 days

[Marc Shin]

Newbie here.  I may make an offer on a property that's been sitting for over 80 days. It's a duplex unit priced at around $325K.  Given the fact that's this property has been sitting for a while, what's a strategy for making a first offer?   20% discount from the current sale price?  or 25% discount?  and then if they say no, do I wait a few weeks and then increase my offer by 5% until they accept?