Thirty years ago marathon racing was mostly reserved for elite runners and fitness fanatics. But as the 26.2-mile event now enjoys mass appeal (some events drawing more than 10,000 entries) never before seen in its history, more and more "marathon virgins" are taking on the challenge. The marathon monster, however, is not to be confronted with nonchalance--it is a formidable undertaking that obviously requires training and also a realistic game plan.
Here's a checklist for rookies that will hopefully help you hit the high notes--as opposed to the infamous "Wall"--in your race:

1.) Build up for battle: Plan on at least 12 to 16 weeks of consistent training (at least 4 or 5 days of running per week) for a full marathon and that is assuming you are already "in shape" for shorter races. A smart choice for your first marathon should be flat or slightly rolling course (as opposed to a hilly one) because the distance itself is challenging enough for your first attempt. Your long run (typically conducted once a week) and some "prep" races are two important "cornerstones" of your training program.
2.) Training partners: Although the "loneliness of the long-distance runner" has a nice ring to it, training partners (at least occasionally, and especially for your longer runs) can help keep you motivated on those days when you might wimp out. Join your local running club or even find training partners by asking at your local running store.
3.) Race ready: It is commendable to finish your local 5K (3.1-miles) but clearing that small hurdle really won't indicate if you are truly prepared for the marathon. A 10-mile race or--better yet--a half-marathon race are highly recommended as part of your training plan (preferably about halfway into your training) to see where you are in terms of preparation for the "full" marathon distance. If you do run a half-marathon, use this loose formula to judge what a reasonable finishing time goal might be for the 26.2-mile race: Take your half-marathon time, double it, then add 10 minutes and that should give you a "do-able" full marathon time to shoot for. For example, if you clock 2 hours for the half-marathon, double it (4 hours) and add 10 minutes: so 4 hours, 10 minutes, would be a realistic full marathon time goal.
4.) Long run logic: Most coaches strongly advise working up to at least 20 miles in training. The long run is also a logical workout in which you can "test" various approaches to the actual marathon, including what to drink (water verses energy drinks), eat (energy bars vs. energy gels or even Gummy Bears) and wear (training shoes vs. lighter racing flats, gloves vs. bare hands, etc.) Also take note during the long run if you have any problems with chaffing, apply some lubricant to address those issues. If you have blisters on your feet, consider that your running shoes might be slightly too tight or small (especially in the toe box), or you need to try a different pair of socks.
5.) Race day: Always have a Plan "B"! You might enter a marathon with a specific time goal or simply to finish the 26.2-miles in reasonably good condition (i.e., buzzing with enthusiasm--not staggering to the finish line in a semi-delirious state!) However, always remember that hot or humid weather situations add an extra burden to even experienced marathon runners--so take that into account and adjust your finishing time goal accordingly once race day temperatures climb beyond 60 degrees. Hydration is always important when running 26-miles (even on cool days), but it becomes even more critical if you find yourself slogging through the miles on a sultry morning. Hit your water/aid drink stations early and often!
6.) 5-star tip: "Pinch" the top of the drink cup--so that it looks like a figure-8 when you bring it to your mouth. This will assure you won't drop it--as sometimes happens if you try to grab it with open palm--and also forms an easy-to-drink-from funnel.