Visualize the entire complexity of the content within the project so that you know what data users will need to access, and compartmentalize those in to separate modules that you can build on over time. Think about any limitations with accessing that data (does the user have that role, what if the data is accessed simulateously, how to handle the same user accessing from different devices etc).
Think about the devices being used - is it going to be a website, an app, both? How best then to access the data? Direct access to a database, or an API system?
Then think about the front-end design and how to simplify the view right down as much as you can. Again, break it down in to modules.
Then decide on the technology you want to use, and what libraries would help simplify things.

These days I like to use JSON API's to access DB content because app and web technologies change quite often but the API will be accessible to whatever I use to build it.

For websites I love using Laravel, which simplifies the back-end tasks, and mdbootstrap which simplifies the front-end tasks and looks "appy".