What factors influence ad-words quality scores ?

The Quality of landing page that is destination url  and amount you are bidding.The page rank and health of targeted website improves quality score and definitely the ad rank. 

hi Gagan,

the main factors that decides the quality score of an ad are epected click through rate, ad relevance and the landing page experience. higher the quality score higher will be your ad position and less you have to pay.

Landing Page content

Proper keywords both in Ad and Landing Page

Preferring the match type (broad, exact or phrase)