If your couple are seeing other togs try and get to see them last. Two purposes, establish they like your pictures (port) and service, discuss what they want, agree to a deal and of course, close it and take a deposit!! ..............
The trouble with being last is that as soon as the couple see someone they like they're just as likely to book them straight away through fear of losing the slot and just cancel everyone else. Of course the chosen photographer will make it very clear that he's taking bookings all the time and it's first come first served. Far better to be in early with a strong pitch aimed at getting them to see you as the person they'll turn to naturally for assurance, guidance and support both leading up to the wedding and on the day itself. I'd go so far as to say that if they don't book you straight away it's almost certain you won't get the job anyway.