Rules are: If you spot a team which is underrated by bookies, you should bet in favour of this team (back). If you spot a team which is overrated by bookies, you should bet against this team (lay).

Example of a possibly overrated team:

The rating is currently at a peak. Question: Is the team really rated correct with this high rating? If you think it is not, you should lay the team. Of course you don't know the future development, but you now one thing for sure: If you bet NOW on THIS team, this is fairly bad. You get quite low odds in comparison to games in rounds before.
Suggestion: Lay this team!

Example of a possibly underrated team:

The current rating is very low. Question: Is it really justified or can this team turn the graph? Of course you don't know the future development - this team might continue losing - but you know one thing for sure: If you want to back this team, the situation is very good. In fact, it has never been better than now, because it is the lowest rating in history and you get really big money, if you believe in this team.
Suggestion: Back this team!