How do I calculate the utility bills if it is the first time for me?
I would ask either the previous tenant, or a tenant in a similar-sized flat to the one youre renting. If (for example) youre moving in on your own - and the previous tenant was also a lone occupier, chances are youll be spending roughly the same. Failing that - just contact the current energy supplier - and be guided by their figures, until you have actual usage readings for yourself.