Yeah i had the same problem when i started to slip the jab to the outside they would throw a lead hook instead. Sometimes however it's better not to duck the actual hook but instead step inside it (if it is a long hook) while throwing a right then bobbing out of the way. The way i generally see it coming is when i can see their left shoulder (as their hand swings out) or when i see their elbow swing out; depending on their technique. But it varies i guess from how they were trained to throw it.