Like you, I've only done 1/2 marathons. I don't plan to do any full marathons, because I have some injuries that are easily aggrevated by too many miles. But what has worked for me when training for a 1/2 marathon is to do moderate runs on Monday and Wednesday, a long run on Friday, moderate run on Saturday, and an easy low mileage run on Sunday (Sunday is optional). I am also a cyclist, so I also do moderate bike rides as well. The key for me is to increase my long run each Friday by about a mile. But it depends on how I feel. Sometimes I will do the same mileage two Friday's in a row, and then bump up a mile the next week.
I have a friend at work that does marathons (and ultra's), and she does bascially the same thing. Before her first marathon, she peaked at about 20 miles for her long run. This should work if you are just looking to finish a marathon. But if you're looking for a good time, then you should continue increasing your long run to more than 26 miles. The key is to allow enough time to reach your peak long run before the marathon. Then, the last week before the marathon, skip the long run, and run at an easier pace on the other runs.