Top tips...build in loads of extra time and contingency in your plan, so if you miss a week or have a low mileage week it really doesn't matter. I had a couple of weeks holiday in the summer holidays were I didn't run further than 5k because I was away and making the most of time with the kids.
What I learnt between my first and second is that fuelling makes a massive difference! I don't like gels so use Dextrose tablets. I swapped water in my bottle for a SIS electrolyte drink too which massively helped with the post run headaches. I also like mini soreens because they're proper food. I also took advantage of anything being offered on the course...mainly haribo!
For me, I run 5-6 times a week, which includes one long run, at peak marathon training I was averaging 40-50 miles per week.
I didn't have a time in mind as I wanted to avoid any pressure, my only aim was to get round comfortably.
It's far more achievable than you think!
Also even if you don't fancy it, eat something when you finish, even if it's just a sandwich and packet of crisps. You'll feel much better, quicker if you get some food in yourself.