I have been running for around 6 years now and whenever I plan on running a marathon I follow one of Hal Higdon's programmes. I find them easy to follow and with nothing too complicated.

Currently I am following Marathon Advanced 2 but I have previously used his other programmes. There are options to pay for extra guidance but there is no requirement. He provides programmes for all distances and I recommend checking them out

If you are up for running more km's per week than what the plan suggests, Hal has said that you can run double up days to add more. For example 5km in the morning and 5km in the afternoon. As long as you follow the base programme he is happy. I was hitting 100km per using this technique and it really felt ok - until my back needed fusing (unrelated). Hopefully I should be back doing this next year.