This is a stub: it really needs adding to. So much to do, so little time!
Obviously the length of your engagement has some bearing on when you start organising but hopefully the following list will give you an idea of what you need to do and when.
One Year
Decide wedding date and preferred time
Decide on your budget. Not very romantic but essential!
Civil ceremony - register the wedding with the relevant registrar
Agree the approximate number of guests for the ceremony and reception
Choose the venue for ceremony and reception
Chose best man and bridesmaids
Start looking for your dress
Buy wedding insurance
Send out save the date cards if you're having them
Eight Months
Draft the guest list
Arrange your photographer, and videographer if you are having one
Buy your shoes
If you're having one, buy your tiara
Agree what the groom, best man and Dads are going to wear
Six Months
Choose music for the ceremony
Choose readings and ask someone to do them
Four Months
Finalise guest list
Three Months
Select items for your wedding list
Send out invitations
Decide on favours
Eight Weeks
Decide on first dance song
Six Weeks
Order flowers from florist
Discuss readings and music with your officiant
Have first dress fitting
Arrange a meeting with your venue(s) to confirm arrangements
Buy gifts for wedding party
Four Weeks
Have your final dress fitting
Chase any outstanding RSVPs
Prepare seating plan
Prepare Order of Service/Order of the Day
Have your hair trial
Order currency for honeymoon
Confirm arrangements with your suppliers, pay any balances owing
Two Week
Let reception venue have your final numbers
Write place cards
Seven Days
Have your hair coloured/cut
Prepare a contact list with number of all your suppliers. Have copies ready for Bridesmaids/Best Man on the day
Collect/purchase any last minute items
Start packing for your honeymoon
Wedding Rehearsal, if you are having as church service
Forty-Eight Hours
Twenty-Four Hours
Take everything you can to the reception venue
Get a manicure
Your Wedding Morning
Have some breakfast
Relax!