I have a game with a menu screen, game screen, game over screen. Do you recommend to use ads in all of them? Is it good for user experience?
The short answer: All ads shown are bad for the user experience. Why would they be good? In a shopping app, they might be useful, but not in a game.
The long answer: It really depends on what kind of ads you're showing and how reasonable they are.
For example, I'd never ever show any ad banner during a normal game screen, if your game involves fast reactions or constantly looking at the screen (like a jump and run or timed puzzle game). If you're doing some kind of simulation that is turn based, this is far less of an issue.
Ads in the menu screen are something different. If they don't distract from the actual game, then I'd consider them okay. The same goes for the game over screen. Just avoid the user doing any accidental tap on an ad banner, as this not only creates a bad user experience ("that $§/%)! got me into clicking a banner I didn't want to click!") as well as possible license/coc violations.
So for a game, use as many ads as possible, but at the same time keep them at a reasonable amount. For example, when I tried "Draw something!", I really enjoyed the game, but finally stopped playing after it started an ad screen in each and every screen transition.
Also try to avoid animated (or even video) ads. Those might get you more money, but at the same time they might keep people from playing your game while outside WiFi range (or simply force them to remove the game).