Here are a few Yellowstone tips.
If you are going to change campgrounds, make the change before 9 am. The roads get clogged up very early in the morning, making travel across the park a slow affair. Campgrounds fill up fast.
Generally the food in the restaurants is bad to horrible. Skip it. The one exception is the restaurant in Lake Village. But I have not been there in years.
Always bring bear spray when doing anything. Always.
If you like hot springs, my favorite is Chico Hot Springs, located 40 miles outside Gardner. Wonderful place, great 4 star restaurant, good deli, great bar but you need to make reservations to stay there about one year in advance. I drop in every time thru. My family loves to stay here.
Do not miss the geyser basins. Upper (Old Faithful) and do the board walk across the river. Middle geyser basin including Grand Prismatic Spring. The biggest one! And Lower Geyser Basin and the drive along the Firehole.
The Firehole river has the distinction of the entire river is contained in a volcano caldara. The entire river.
Lots of good fishing everywhere. I like the Gibbon and the Yellowstone rivers best.
Go to Artist Point just off Canyon Village. Don't miss this.
Dunravean Pass is the best place to watch for bears.
Everything towards the eastern edge is extreme grizzly habitat. The Absorka range is full of them. The camping on the eastern side (outside of the park, near Cook City) is hard shell camping only.
Don't miss Grand Teton National Park! These are just a few suggestions.
Tim -out