Do not use a real password
The first beginner tip is also the most important safety rule: never type a real password. The game is a puzzle and the input should contain experimental text only.
Use simple chunks that you can recognize and move around. A password made from small pieces is easier to debug than a long sentence with hidden conflicts.
Keep your password flexible
Early rules can tempt you to create something neat too quickly. Resist that urge. Later rules may need a month, country, element symbol, binary string, NATO word, or perfect square.
A flexible password gives you room to add these pieces without rewriting everything from the beginning.