Do contact your celebrant early - several months before the date you have in mind for your wedding. Celebrants can be very booked out at popular times.
Documents for the Celebrant
Remember that you must give your celebrant the "Notice of Intention to Marry" over a month before the ceremony, along with both your birth certificates. If either of you has been married before, you must also give your celebrant official evidence of your divorce, or the death of your previous spouse, along with your birth certificates.
Choose venues for both the ceremony and the reception many months ahead, and contact whoever will book those places for you. Many outdoor venues require permission from the local council. They will usually then book a particular spot for you. In some cases there is a charge, in other cases not. Some other outdoor venues must be booked through the managing board eg King's Park Board. At this time you can also ensure there will be power if you need amplification or lighting.
If using an outdoor venue, do make sure you provide some chairs for those who cannot stand for long, and that these people (eg grannies) can access the spot easily.
Also make sure there is shade in the summer, and shelter from rain in winter.
Check parking availability, and let your guests know about this.
Browse the shelves at local libraries and specialist bookshops for books that suggest ceremonies and wording.
Think about what you would like to say in your vows, and jot down some ideas on this to discuss with your celebrant.
Check the internet for ideas on "sustainable" weddings.
Consider taking a "Marriage Preparation Course". There are many available now (see the internet) and such a course can save you a lot of pain in the early years of your marriage.
No-one's marriage is problem-free, and prevention is so much easier than cure!