I came across John Maeda’s 10 Laws of Simplicity back in 2011 and I think they have stood the test of time. Here’s a link to his site:.
Ten Laws of Simplicity
John Maeda
1 Reduce
The simplest way to achieve simplicity is through thoughtful reduction
2 Organize
Organization makes a system of many appear fewer
3 Time
Savings in time feel like simplicity
4 Learn
Knowledge makes everything simpler
5 Differences
Simplicity and complexity need each other
6 Context
What lies in the periphery of simplicity is definitely not peripheral
7 Emotion
More emotions are better not less
8 Trust
In simplicity we trust
9 Failure
Some things can never be made simple
10 The One
Simplicity is about subtracting the obvious, and adding the meaningful