Don't just visit your local tower, any applicant should visit the an Area Control Centre as well. Most controllers end up there anyway and, whilst you need to appreciate the WHOLE ATC picture, that's where the REAL work is done! One applicant, who'd spent some time working in ATC, completely threw away an interview because they didn't know how aeroplanes navigated across the oceans! There are several good books on ATC; read them!
