A brilliant blurb is an excellent draw for me to buy the book it is on. Tricky to write though! (I do think writing flash fiction regularly at least gives you practice in writing to the word count required for blurbs but I am biased here given flash is what I do).
What I want from a good blurb is a taster of the book. I must have an idea of who the lead is and the problem (the major one) the character is facing. I have then got to feel as if I must read on to find out what happens. If successful in making me do that, the blurb has done its job!
Blurbs are best kept short. You do just want a taste, not the whole buffet, but it has to be enough of a taster and that is the tricky bit to get right, I think.
Mind you reading lots of books and seeing how other authors have done this is a great way to learn for when you hopefully get to do this for yourself!
Not that I need encouraging to read more, mind you. That is always a great thing to do whether you write as well or not.