You are something that we, as writers, should try to avoid making our readers do unless the reason they are yawning is because they're so engrossed in a book that they're up half the night reading it. Yawning because they find the book boring--we want to avoid that as much as possible.
There is no magic solution to creating a non-boring book. Everyone has different tastes. What I find terribly exciting when I'm reading might be boring as all get out to someone else. That's okay. But if every single person reading your book is really bored, something needs to change. There are many different ways to spice up a book a little--it depends on what you're writing, genre, characters, world, situation, etc.. What's "exciting" in an adventure story is going to be very different from what's "exciting" in a romance.
Here's hoping that most "yawns" from readers are ones of exhaustion from reading too long and not yawns of boredom.
*As I mentioned, everyone's idea of exciting is different. What kind of stories do you write, and do you have particular things you do if you feel like your writing is starting to drag? Do you cut some things? Do you throw in a twist and have something unexpected happen?