What do I have to do to have high quality food or drinks?

Every business can be set to be high, medium or low quality. You can change the quality by tapping on a business to select it and tapping the info button (the blue button with the 'i' on it). You'll see a section saying "Product Quality" that gives you three quality options. Simply tap the circle beside the quality level you want. 

Guests prefer higher quality but the higher the quality the more supplies you need to use so choose the quality level carefully!

Some goals ask you to serve a certain number of guests at a particular quality level e.g. Serve 15 high quality meals at the Rustic Restaurant. In this case you need to set the quality to high in the Rustic Restaurant and wait for enough guests to use it. Make sure that the business has enough suitable guests nearby. Only guests staying within the catchment area of a business can use it. You can see a business' catchment area by tapping on it. It's the green square. Businesses need to also be the right quality and price for a guest type so they can use it. To see what guest types can use a business, tap on the business and then tap the info button to open the info panel.