Before you start designing or building a website, or really anything, it can be helpful to first spend time establishing rules that guide that process.
Then, anytime you design a new component or functionality, you make decisions that follow the rules you've set.
An example rule might be something like:
Any element that communicates information or state must have at least two distinct methods of doing so.
This rule helps ensure that you're adhering to the WCAG Use of Color guidelines.
Maybe you also set a rule that says:
Lines of text must not be longer than 800px.
This rule can help avoid readability issues caused by long line lengths.
...
This can obviously get out of hand and you could quickly end up with a list of over 1,000 rules. But if you start slowly and add to the list over time, the rules you create for yourself will soon be second nature.