Think about the mistakes Harold made during his campaign. Remember to provide examples.
Your final paragraph before your conclusion should look at the weakness of the English soldiers.
You must now decide if one reason is more important than the other or maybe there is a combination of reasons to explain why William was able to win at Hastings. Do some facts link up with others e.g. if Harold had not had to march all the way to the North and then all the way back again his soldiers would have been better prepared and William's men would not have been able to get ready to fight as quickly.