The Trick is to do a strong Contest of Mayors, and at the next contest get the minimum amount of points in order not to go down in the League. That is to say, one week you go strong, the next do to the minimum, the next strong, another to the minimum....
By doing this you will find that the opponents are easier when you are trying to get the first place in the League.
There is an explanation for this. And it is that the mayor matching (which is a computer algorithm), tends to associate in a league, not only those who have the same level of experience, but also those who have had a similar level in the previous League (that is, in the previous week). So if you do the trick, when you want to do a Contest of Mayors to win, you will get more affordable mayors, and when you go to do the minimum, you will get strong mayors (but you won't care).
Notes: when it is the week of doing the minimum, it is important not to go down in the league. In the image on the left you can see that the first in the metropolis league has only 16,475 points, with 12 hours to go, which is very easy to overcome; and with only over 8,700 points you get the third place.
Important: from time to time (at the end of a Mayors pass), double plumbob points are earned. In this week, many people are encouraged to do the Contest of Mayors, so this trick at that time does not usually work too much.