First of all congrats!!! How exciting.
It all really depends on how much you like planning, money available, number of people and most importantly WHEN you want to get married.
I know for us, we were paying for it ourselves (both of our second marriage), so I wanted to make sure it was far enough out there for me to be able to budget it out. I booked everything pretty quickly and am making payments according to due dates and number of pay periods left. If you have parents paying for it, then it will be easier to make quicker decisions.
First thing is get a general idea of when you would like it and what “style” you would like (elegant, ballroom, rustic, barn, vineyard, etc), then try and sit down and come up with a preliminary guest list. Get with your parents if they are paying or have input (usually typical with first marriages).
SET A BUDGET!! There are sooooo many things that add up quickly. I found that the budget planner on theknot.com really helped me get started on how much to allocate for what. There are a lot of costs involved that you might not think of. If anyone else is contributing you can factor that in.
Once you have a date, style, budget and number of guests, then you can start looking for a venue you would like, since some have a minimum and maximum for number of people. All venues will ask you when and how many people. Then the other vendors will ask you about budget. Once you have your venue booked, then you can look for your other vendors.
Talk open and honestly to your fiance about realistic expectations and include him on all of it (or at least ask him what he wants to be included in on and or run it by him).
Try and enjoy the engagement and the planning together. Take a few weeks before starting but have some general talks to get it going. It may be too much for him too fast otherwise. I know mine was getting overwhelmed so he just asked that I put all my questions for him together and we have 1 night a week that we sat down and went through everything that dealt with wedding. Now that it’s all booked, he’s definitely a lot more easy going about questions/problems.