What do you want your website to look like? Consider websites that are similar to the one you’d like to build, ideally in the same industry or serving similar types of customers. Build a set of examples of types of pages, design aspects, and website features that you can hand off to the web designer — the person you hire should have experience creating websites with the features you want. If they don’t have the right skill set, they’re not the right pro for you.
The words in the tag should be more than a description. They should provide a text equivalent of the image. In other words, the tag should include the same meaningful information that other users obtain by looking at the image. In the example of the mayor’s picture, adding an “alt” tag with the words “Photograph of Mayor Jane Smith” provides a meaningful description.