Originally Posted by bitpuddle

Just enough to hold the headset together. As soon as you can apply the front brake and rock the bike back and forth without movement in the headset, you’ve tightened enough. Barely more than finger-tight.

If your headset loosens, you might have issues with the frame prep (head tube not faced/parallel, unevenly reamed, too of steerer not cut at 90 degrees, etc).