Moving self hosted site to a new host

Hell and HEEEELP!

I am trying to move to a new host, in my naive way i thought i could just take my complete backup and be up and running on my new host….I have since discovered that no this is not the case. All i get is a page saying there is an internal configuration error.

Can someone give me a step by step quick guide as to how to do this?
(I hope this is not mission impossible? surely people must have had to move hosts and servers before?)
Many thanks

Stuart