Training for a marathon is going to mean dedication on your part. Marathon training is a long term pay off that has a number of rewarding milestones (like achieving half marathon distances regularly for fun / training) but requires planed training runs that slowly increase your mileage over the course of 5-6 months to condition your body to be able to handle 42.2KM when you need to on race day.
While you may have been able to just go for runs here and there or log regular treadmill time to complete 5-10K races you will need a strategic plan to ensure your gradually increasing your mileage while getting the fitness adaptation and recovery cycles that are necessary for full marathon training without injury.
To accomplish this I would suggest the use of an established training program based on your current fitness and goals. Such programs are in abundance online etc. But for you your first go around at the marathon make sure you select a plan structured and realistically suited to your current fitness ability and is geared for a first timer.
RUNNING GROUPS: COACHING & COMMUNITY
A very popular option for training is joining a running club / training clinic at stores like the Running Room or charity training programs like Team in Training tapping in on the set schedules, tested, coached training programs and community training atmosphere that can get you through the training miles and will probably give you some running buddies to head out with on race day.
These types of group runs are also an invaluable learning experience if you can only attend them even one in a while. Drop in clinics such as the CRS Tune Up Runs for example allow you to talk to other runners and hear them share secrets to questions you may be having with your training etc.
Sign Up For Running Clinics: STWM Running Clinic Page
There can be a downfall however to these types of group / fixed time training programs. If you are like me and work / life in general will likely get in the way of you getting to clinics regularly at specific time, or like I was starting out and you were a little intimidated by heading out with a group at first then you may need a different approach. If this is you, you may find yourself more of a lone wolf training at odd hours, for this I suggest a digital coach.
DIGITAL COACHING: LIKE HAVING A TRAINER WITH YOU ANYWHERE
Using a digital coach can help you avoid some of the pitfalls of losing motivation or cheating on your training runs as can happen following a training plan on your own as a novice with no outside feedback. There are number of websites / apps that can help you in this area if you do a little research online.
I personally used the Adidas MiCoach app to train for everything from 10k to a Full Marathon in my first year of running. The MiCoach software (micoach.com) and others like it run on your smartphone using its GPS to gauge your speed, logging your runs for you online as many apps do but with a couple big differences.
The first being that you setup the running app on the MiCoach website and select a training plan for the event you want to run, and then input the date of that event, the days you can / can not run based on your schedule for an average week etc.
Then MiCoach makes a training schedule for you that lays out all of your training for the months leading up to race to ensure you have a safe and structured training plan much as you would running with a group or team that is flexible to running anytime of day, and you can even move around a little.
The second major feature of this training method is that it’s tailored to you specifically setting your running paces etc based on your fitness by the MiCoach software giving you a 12 minute running test on the first day out. This assessment like all your training runs is guided by your “Coach” which gives you verbal instructions via headphones on your run.
The assessment data is then used to tune your training plan in to pace / heart rate zones so that you can build up to the marathon mileage safely and realistically based on your existing fitness level with a plan that works to ramp your mileage up and down accordingly.