Use Open Sans for body text, it's the only sane choice.

Use bold text when you want to be heard, not when you're just shouting.

Use #f7f7f7 for backgrounds, it's not too bright.

Use #333 for text, it's not too dull.

Use 4px borders, it's the only size that matters.

Use a grid that's not too grid-like, it's a delicate balance.

Don't animate anything, it's a waste of time.

Unless you're making fun of animation, then go wild.