all colleges run differently with regards to their recruitment policy and how they interview and assess their prospective students.
most will include some kind of assessment to see where your english & maths skills currently sit at, and possibly some kind of 121 interview just to see if you have any further questions, and so they can see you are applying for the right course etc.
as for preparing yourself... ask yourself why are you applying for the course? what do you want to go on and study at uni? and what have you done previously etc. they will probably ask questions like that. just show you're keen and you're determined to succeed.
to be honest most FE colleges are pretty lax with their recruitment of new students and tend to accept most people that apply, they need the funding.