Start planning as soon as you become engaged.
Make a list of eveything that you think that you want in your wedding and as the date draws closer you can rearrange and eliminate the things that are no longer important or necessary.
Look through magazines to get ideas on wedding and reception styles.
Decide what you can live without in the wedding and what you must have, then you can start to work towards that goal. ex., a fancy reception which means that you may have to cut down the cost of flowers, bridal party, expensive favors, etc..