Lots of different layers. That, and having multiple pieces, so you can tune your outfit to the conditions.
I like to 'start cold' as I tend to warm up pretty significantly once I'm under way, and I'd rather be slightly under-dressed when participating in an athletic activity, than over-dressed.
Remember, too, that daytime temperatures often increase quickly in mid-morning, so you may spend most of the ride carrying more clothes than you're wearing.