3) The Seasons
Regardless of which region of the country you live in or the wedding will be in, you need to consider the seasons and weather. How much you need to factor it in, depends mostly on your location. For cold weather climates, selecting a warmer month vs. colder month will be the initial consideration you need to make.
Also consider the general temperature for that season and how much it typically rains in your area. Always have a solid weather back up plan for your guests. Period. End of story. It's your responsibility as the host of this event to ensure that all guests have a safe place to go in the event of inclement and/or unsafe weather.
Remember that weather is the one thing that no one can control on your day. Selecting a given season isn't a guarantee you'll have beautiful weather. On my own wedding day, I had researched weather almanacs going back 50 years and our average daily temperature for that date had never been below 60 degrees. Come our wedding day, the temperature forecasted was 40 degrees! Selecting a season can also help guide the vibe and overall feeling of your day.
I recommend ruling seasons out that you definitely don't want to get married in, and then looking to your venue availability or the other factors listed here to help you choose between the remaining seasons.
4) Overall Guest Travel Needs
If you have a significant portion of your guests traveling from out of town for your wedding, consider their potential travel needs when picking your date. Google your city name and potential date and see if there are any big events happening that weekend that would make airfare, hotels, etc. more difficult or expensive. Consider seasonal travel needs if your wedding is at a particularly difficult travel time (such as: dead of winter, major holiday, summer tourist influx). If your prospective date falls during a more difficult time for guest travel, make sure to give your guests as much notice and possible to make arrangements. Plan to communicate early and often with them about the travel needs and what to expect.
5) Your Future Anniversary!
I don't think this gets nearly enough consideration when couples select their wedding date. Your wedding happens once, but your anniversary happens EVERY YEAR and is a special occasion that you and your partner can connect over again and again throughout your lives. Think about how you may want to spend your future anniversaries and what your life typically looks like during that time from year to year.