A lot of authors will tell you to write a certain number of words a day, to plot a book to have a specific amount of words by the time it's done. But I guess I'm not like a lot of authors, because I'm going to advise you to do the exact opposite. If you try to write within some sort of weird word count box, you're not really writing. So stop worrying about the word count. I'll tell you why.
No, I'm not contradicting myself. All my feelings about overly-long books still stand. Overall length is still an important consideration, but not so important that you should be thinking about it every time you put your fingers on the keyboard. Because when you try to write to a certain word count, you're really stifling yourself. And for a writer, that's no good at all.
For most writers, it's not good to give yourself a daily goal that you must hit. It's not good to constrain a book to a certain word count, because you think all YA fiction should fall under 80 thousand words or less. When you do that, you're putting limits on your own creativity. And why would you want to do that?
You can't put limits on your book. At least, not on the first draft. The first draft is your chance to write at will and tell the story you need to tell. When you're editing, you can worry about length and cutting down on word count when it gets too long. But writers need space just to write. So stop worrying about the word count, and give yourself that space.