Well, to the extent that I progress my long runs over the course of a training cycle, it starts off with my normal 14-16 miles early, then it goes up to an 18 miler near the start of the main part of the training cycle. After that, it becomes a matter of alternating between straight long runs (run at only easy distance pace), TLT runs (long runs with a tempo portion mixed in, usually in the beginning and at the end, but just at the beginning at the very start of the cycle), and marathon paced runs.
The first step in that progression is a 2 mile warm up, 4-6 x 1 mile at tempo pace with a minute rest, 8-10 miles easy for a total of 16 miles or so. I then go to an 18 mile straight run, then a 20 mile straight run, then a TLT with 2 miles up, 4 x 1 mile at tempo w/1:00 rest, 10 miles easy, 15 minutes at tempo effort, cool down to 20 (that is what I have on the books for this weekend). Then I go to my first run at marathon pace, which is 2 up, 13 at MP, 2 down for a total of 17. It is hard to see in this format, but the essence of the progression is to get used to the straight distance first, then work in tempo at the same or a slightly shorter distance, then increase the distance again, then work in tempo at that now increased distance.
The 13 at marathon pace is really rough, and I have discovered the best way to make these feel manageable is to find a half-marathon race to sign up for and run at marathon pace. Being in a race setting, with closed roads, clocks, water on the course, competitors, etc. just makes it a ton easier. I try to do 3 of these runs per cycle, and I have always done at least one of them as part of a half marathon, and I would prefer to do all 3 that way. I would say that finding a half to do the MP runs in is the best piece of advice that I could give you.