Ads are a vital part of monetizing F2P games. As a developer you need to balance maximum exposure for the ads you integrate on the one hand, and ensuring an immersive game play experience on the other.
Rather tend towards less ads. Your players will thank you by sticking with your game longer, potentially being exposed to more ads, than if they quit your game after a few minutes of being bombarded by ads.
What message do you communicate to the player, if the first thing they see in your game, is a startup ad? The only time to use a startup ad, is if you have no confidence in your game and you know the user will probably uninstall it straight away. Well, at least you got one ad impression.
If you know that your game has reasonable retention, try to only present the user with ads on the second or third day of use. Give the user time to get engrossed by your game without the distraction of ads.
Although their popularity is on the decline, overall, banner ads still make up 40% of the potential ad revenue.
The key is to use them correctly. Banner ads are best used in slow games. Word or puzzle games give the user time to notice an interesting ad and click on it. Fast paced action games do not give the user time to even take note of the banner ads presented. Even if they do, they will surely be reluctant to interrupt their high-score chase to click on an ad.
Use these at logical breaks in your game. After a game over scene is a good time to show an ad, however, avoid showing an ad every time.
Ad networks have extremely sophisticated routines in place to prevent abuse. It is very easy to make mistakes during implementation, which can lead to your app being blacklisted by the ad provider, or even your account being suspended.
Do not cycle through ads too fast. If you refresh your ads faster than the specified display time prescribed by your ad network, then the view will not be counted as an impression. This is seen as inventory burn by the ad network and your game will get downgraded, getting served progressively lower quality ads.
Even more dangerous is a high click rate, but low install ratio. The ad network may assume that you are either tricking the users into clicking on ads, or the users accidentally click on badly placed ads which they are not really interested in. This can quickly lead to a blacklisting of your app or even a suspension of your account.