Pre-built themes to start from:
But once you have a starter theme, where do you go?
Create some wireframes for your site. Figure out how it should look on wide windows and how it should look on narrow windows, and how the various elements on the page will rearrange themselves from one to the next. Build the site. Build your site mobile first, so that phones have to do less work.
You should wireframe, at minimum:
Don't hide stuff on mobile. Instead, add stuff on desktops. Your readers shold be able to learn everything they want to from their phones or smartwatches. The best way to do this is through progressive enhancement.
Always, always, always be testing. Try things on different browsers on different operating systems. If you have a Mac, install Xcode so you can use the iOS Simulator. Don't have a Windows machine? Get a Windows VM with Internet Explorer at modern.ie. Don't have an Android device? Try the Android Emulator that comes with Android Studio.