With a well-written back cover you can already start promoting your book. You can also approach publishers, sponsors and potential buyers, ask for feedback from future readers and start the presale! Plus, your back cover gives you the structure to write the rest of the book without getting stuck.
In the video below I give tips and share my experiences.
Oh, before I forget: the back cover is usually about 250-300 words. That is much less than you think! So write and DELETE very smart! 😉