I learned that it's important to have a game plan centered around a budget. Be realistic and discuss this in advance with your fiance before booking any of the vendors. Cost of weddings vary a lot, depending on where you are (city), what type of venue you want (backyard vs. hotel banquet hall vs. country club vs. winery vs. other), the date/time (weekend/holiday v. weekday; luncheon v. dinner) and all the details you want. I have to admit that it was hard to even set a budget without knowing how much things are supposed to cost. Who ever tells you these things? Ask your married friends for advice. They will definitely have lots of information for you. But just remember: you don't need to (and absolutely shouldn't) break the bank to have a beautiful wedding day.
To plan = To research. Research what's available to you that fits you and your fiance's style. I used Here Comes the Guide (http://www.herecomestheguide.com/), Yelp (http://www.yelp.com/) and various other websites for vendor reviews. Call potential vendors for pricing and maybe even visit some of the venues & vendors. This may be a good time to also prioritize what elements of the wedding important to you and your fiance (ie. number of guests, venue, food, photography, entertainment, etc). In the meantime, also be thinking about a date. I would recommend at least two or three possible dates (be flexible) so as you contact potential vendors for info, you can also check on their availability.
After some initial research, you may wanna go back to the drawing board and revisit the budget. Make some adjustments or give yourselves an amount "plus/minus [insert your amount]" when coming up with a working budget. This way you'll have some wiggle room and not feel so constrained. Don't forget to factor in taxes and tips as well! And again, be realistic and flexible as you guys are deciding what you want - ie. if you decide to spend more on one vendor, be deligent about cutting back in another area to balance out the expenses. Brilliant planning will surely give you a beautiful celebration!
To get you started, here is a checklist/timeline from RealSimple.