Hello Jk, always follow the level of the existing floor and sit it flat against the floor, you will have to accommodate for this un-level floor when you cut your internal scribes and external mitres don't try to get the skirting level because over a long length It will sit flat one end a be off the floor the other and ...

Should there be a gap between skirting and floor?

With carpet, skirting boards can be fitted to the floor. With laminate or tiles, there is the requirement of a small gap between the flooring and the skirting board. Therefore, skirting boards shouldn't have any contact with the floor and should be fitted after the flooring has been installed.

How do you fix uneven skirting boards?