Well, the first thing was to accept that it would take years. And the second thing was to work out a rough timetable. My goal became to write a canto a month—in other words, to write at least thirty pages a month—approximately a page of poetry a day.
Now, you need to realize that the month of composition may have to—and, indeed, did—involve further research. For example, Spenser takes his family from Cork to London by ship. What was the nature of an Elizabethan ship? What kind of ship? Where would they be housed in the ship? What did the captain and his crew need to do, particularly if the weather changed? What was the route? And so on.
But I tried to keep to the schedule, and for some shorter cantos actually succeeded.