There are three main categories, including selling your product or service, establishing trust, and a call to action.
Sell your product or service:
This is where you can start building your unique selling proposition. The main headline can be anything that makes sense for your product or service. It can bring a specific problem a user has to focus which your product or service can solve, or it can simply promote your product or service right away.
For example, there's a big difference in how you would sell a big aeroplane engine versus a candy bar. One audience expects a really detailed explanation while the other just wants to know that your candy bar is delicious.
Establish trust:
If you're pulling your testimonials from websites such as Yelp or Facebook, you might even consider pulling the star ratings to showcase the overall score. Don't forget if you're doing this to also implement schema mark up so that your stars show up in search engine results.
If your industry has any accreditation bodies, it would be a good idea to try to get accredited sooner or later. Not only does it help you in gaining more trust with your customers, but it will put you ahead of your competitors. If your competitors are already accredited, then you need to become accredited just to stay on the level playing field.
Call to action:
Whatever your call to action is, you just need to have one and it needs to be simple, easy, and quick for users to complete. If your call to action is obscured or difficult, then everything you did to sell your product or service has been done in vain.