You can pull these straight out of your Ideation Stage exercise. Customer segments are the groups of people or businesses that have a problem that your product or service will solve. You can take your existing customer base and break them down further into geography, gender, age, behaviors, preferences, interests, etc. so that you can meet their needs with even higher specificity.
As you look at your customers/audience, stack rank them to see who you should focus on first and who you can focus on later or ignore altogether. Once you have the segments, create customer personas for each. This persona can include their worries and fears, online behavior, professions, influencers, hopes and dreams, desires, and what would make their life easier.