How do I build my credit score back up fast?

So I had my credit score at 700 but when work slowed down I had no choice but to use my credit card and I did max it out but I ALWAYS pay it off in big payments. Since I did over spend, my score dropped over 20 points, it’s currently at 669 now.

My goal is to get a credit score of 800, but I need help, I have no idea how to build it up fast.

The balance to use on my credit card is $700 so how much do I have to use in order to build my credit up? And not only that what else do you guys recommend to build up credit?

Also how long do inquires last? I have 6 inquiries on transunion & 6 on Equifax. They were from applying to credit companies, car dealership & a jewelry store.