Whether people are searching from their phones, their car's GPS, or a device such as Amazon Echo, it's becoming increasingly common to speak queries out loud rather than type them into a search engine. Google is paying close attention to this trend and is making adjustments in how it ranks sites and presents information.
One basic principle to keep in mind is to think of how people naturally ask questions. SEO is moving away from written queries such as "pizza downtown Austin" to more natural ones such as "Where is the nearest pizza place?" (Increasingly, searchers don't need to specify the location because their GPS-equipped devices know exactly where they are.) Voice searches are often questions as opposed to keywords.
Another thing to know about voice search is that featured snippets are now a major factor. When you search for a term on Google, you can see featured snippets from a lucky, SEO-savvy website. How do you optimize your site to be featured by Google as a snippet? Focus on FAQs that searchers have about your industry. Remember, Google is looking for a quick and accurate summary of the information searchers are seeking.