How to move from UK to Canada or America?

I was wondering what is the best course of action to take when one is considering a move to another country, specifically from UK to America or Canada. There are various factors that should be considered so any help with any of them would be appreciated.

Who to contact or speak with for information

How to get assessed for eligibility

What visa to apply for if one requires to ability to work in a specialist field (IT, Networking, Graphics/Web development)

What areas or cities to consider (Strong IT sectors)