Congrats hun, Think about the style of wedding you want, go to wedding fairs to get some ideas, you really need to think about the date and budget to see what time scale that gives you for planning and saving!! Numbers of guests then like the other girls have said, the venue and if you are getting married in a church you need to speak with the minister to arrange that if you are getting having a civil ceremony you will need to book the registrar (£29) and then you are able to give your notice no more than a year before your chosen date (the notice lasts for 12 months from the day you give it). the tog entertainment and florists are often the first to get booked up so if there is something you really want then go for it asap (but dont make rash descisions you may regret!).
I had booked pretty much everything for my wedding by April, more to try and secure a good price and get the things i wanted on the day we had chosen.
One last tip if you ever need us we are here so drops us a line good or bad!!!
Good-luck and happy planning!! x