Content-first design helps us to think about the real design opportunities and constraints. It also means that we take into account the design implication of different languages, e.g. German words are usually longer than their English translations. When we work with real content in our design plans (whether it is a Sketch, a Wireframe, or a Prototype), we can use different sources: if it is a redesign, we can start with your existing content. We can also come up with our own texts (based on the things we have found out thanks to UX Research and to analyzing the data collected during the Research), and we can also start testing with your competitor's content, just to create valid starting point for test and iteration. So Content Inventory and Competitive Analysis are useful methods to conduct for the purposes of Content design. It needs to be highlighted, however, that we are not native English speaker. We can help with copywriting, but we suggest you to have a professional copywriter as well.
Carefully planned Information Architecture (how the content is organized), readability (the content should be easy to scan) and accessibility (for example for screen reader users we need to provide alternative texts instead of images) are also important factors for a successful Content design. Emotional design also plays an important role here: the images, videos, animations, illustrations, the tone of voice make an impression, evoke emotions. You also need to think about conversion optimization: the content should contain the most important keywords. As you can see, there are many aspects of Content design, thus it has a huge impact on the UX of your digital product.