Harold spurns all your reasons for demanding that he relenquish the crown that he agreed two years ago belongs to you. So it is to be war then. You feel fully justified: Harold is a perjurer, having broken sacred oaths taken on holy relics before numerous witnesses. You can add to that a list of the women he debauched while in Normandy; he is an adulterer. His word means nothing, and telling everyone that his people must hate him might go a long way. You start a smear campaign, blackening Harold's name in every way possible; he deserves it. Your best stroke is sending word to pope Alexander at once, of Harold's broken oaths: making sure that the pontiff understands just how spiritually backward England has become ("archbishop" Stigand of Canterbury is a good case in point, refusing for many years to allow any papal legate into England, and keeping his see of Canterbury without canonical appointment).
Preparation for invasion is a mighty undertaking. Of course you need ships and troops. The details of such could fill a sizeable volume. By summer's end you are ready and your fleet and army are waiting in the Dives estuary for the wind to change. You have difficulty keeping so many thousands of men occupied while encamped for so long. Daily military drill is the best time consumer. Still, there are desertions, and these increase as the season grows late: men are beginning to believe that you will disband and wait till next year. Maybe you should. If you cross now (late September), how much time will you have to bring Harold to battle and beat him? The prospect of campaigning throughout winter in a hostile England does not sound good at all. What can you hope to accomplish in a few weeks before the cold storms of winter make warfare impossible?
Disband your army till the following spring.
Force a crossing in the uncertain wind conditions prevailing.