new sieges are whats counted, exisiting sieges dont and removing a siege subtracts the points, if you are going for siege ranking its best to reset every other week and go for it fortnightly 

It's very easy actually, and Mortee is right be she should have been more precise ;)

The only way to get points is to besiege cities, so you have to have a few thousand javs for instance and send them endlessly to low level (obviously abandoned) cities, and that's it.

You do that from a Monday morning on (in Europe), and the next Monday, you can recall them all at once (you will lag a little!), but don't do it two weeks in a row because all the sieges that you recall will be counted as negative points, so you will have to do twice as much the second week to get just as many points

Thanks for the clarification lefeubleu :)