American football in the UK is an amateur sport so if you want to turn professional you have to look at the NFL in America or NFL Europe. There is a thriving scene in the UK though and many chances to get involved.
The best thing to do first is to watch a NFL game on TV. This will give you a feel for the physical nature of the game and help you decide if this is something you want to do.
Although Rugby and American Football are two different sports the best and easiest way to get ready for starting American Football is by playing Rugby.
The next thing you need to do is find your nearest American Football team.http://www.bafa.org.uk is the website of the British American Football Association and you should be able to use it to find your nearest team.
Whilst you are learning the game buy yourself an American Football and practice your catching and throwing.
American Football is getting increasingly popular in colleges and universities in the UK with many starting their own teams.
Find your best position and dedicate yourself to learning that role.
Do the necessary exercise to get yourself in the shape you need to be in for your position.
If you have dreams of making the NFL inAmerica the best way is to get a scholarship to an American College. A scholarship is when the college pays you to attend as they want you on their American Football team. 99.9% of NFL players are picked from American college teams.
To help you win a college scholarship get someone to film one of your games so you can send it to America.