Themes set the mood for your online space so it is important to choose one that feels right. There is no one-size-fits-all for themes and if you have more that one website, chances are that you will also have more than one theme. From the technical side, the theme should be responsive so it looks as good on mobile as on the desktop. You want to make sure that your theme is being supported and updated regularly and that it has a good reputation and reviews.