Deepak: I believe you meant Quality Score of Adwords and not Ads as Quality Score is an attribute of a Keyword. Given Quality Score is a measure of user experience for a searcher on Google, it is affected by following parameters:
CTR (Click Through Rate): CTR of your Ads is one of the key parameters which affects your keyword Quality Score. A great ad copy should take care of following aspects: a.) include keyword b.) highlight the benefits for the user c.) call to action
Ad Relevancy: How relevant is your ad for the keyword? Having keyword in your ad copy is must for you to improve your quality score.
Landing Page Relevance: How relevant is your Landing Page? To improve relevancy of landing page, you should take care of following aspects: a.) include keyword to make it relevant b.) should load quickly c.) easy navigability d.) originality of content e.) trustworthiness
If you take care of the above parameters, you will be able to improve your Quality Score and thus improve the position of your Ad and reduce Cost Per Click (CPC). Hope this answers your query? Let me know if you still have any confusion about improving Quality Score.