Choosing Colors, Design, and Layout
I strongly recommend using a color tool such as Paletton, Adobe Kuler, or Color Combos. Colors can affect how visitors feel about your credibility or if they buy your products.
A good way to get inspiration is to look around at other websites that use similar business models and have a similar product environment. Start by figures out what different pages they have, how they set up their navigation, and how their content is organized.
Some principles to consider are consistency, efficiency, simplicity, usefulness, and appeal/motivation.