A good quality score on your keywords can be brought about by making sure that your keywords are highly relevant to the adverts that will be displayed, as well as the landing page on your website that you are directing people to.
An area of optimisation that I use regularly is to break up Ad groups into small, highly targeted groupings, rather than placing all your keywords into one place.
An example of this would be if I was using Adwords to get people to see my services, keywords would include: SEO Optimisation, Google Ads Optimisation, Web Design, and Social Media Management.
If I was to use all those keywords in one Ad group, what advert would appear? If a Google user was searching for SEO optimisation and an ad appeared talking about Social Media Marketing, then there is an instant disconnect between what they have searched and what I have shown them.
This would lead to a lower quality score than it would if the Ad text matched the search term.
Quality score is also affected by the web page the visitor lands on. Again, the relevance of the content is what the quality score is based on. A common mistake that affects quality score is an advert that goes directly to a home page, rather than the service page that contains detailed information about the specific search query.