Stay in gear.
Don't coast downhill or towards lights in neutral as this uses more fuel! Stay in gear and ease off the gas gently to reduce fuel flow to the engine to virtually zero.
Jeremy Clarkson has said the same on a Top Gear when he had a fuel-saving challenge. I've even tried it myself with the instant fuel consumption gauge on my dashboard, and they're right... so you're actually using more fuel and driving in a dangerous manner if you're deliberately coasting.