Simple is good. Players have enough complexity internally already.
If a token is called for, ideally that token should be edible.
If your game needs a scoretrack, then you are doing it wrong. Game position should be visible and intuitive.
Three big questions (What is it about (theme, not setting)? What do the characters do? What do the PLAYERS do? How do the rules enhance these things?) are useful.
Playtesting is good.
Better is the enemy of done.
Emergent behaviour is good. Very good. But it's also worth documenting (at least in notes), because other people have different base assumptions.
If there is usually something in a UI slot, there should always be something there. Even if it's some form of zero. The invention of zero was important and useful, in this case if only to prevent miscommunication. Use it.