It really depends what sore of runner you are.
When I ran 2:25, last 6 weeks I did lot of running at Marathon pace.
I had this hilly course on pavement where I did 10 miles at 5:30 pace and usually whatever I can average with 90% of MAX HR for those 10 miles , was what I ran few weeks later.
Also lot of slow running between worked for me. So like typical 70min/40 min doubles every day, and you can change them up. I went at 8:00 min a mile.
Long runs I did 24-26 miles once a month very fast so I would run a marathon at 2:35 one month out while practicing drinks.
I would take 3 days easy recovery runs after that. When I ran 2:35 in practice with HR that I desired I knew I can go 2:25, so I guess its about mental aspect as well.
I also did lot of long runs at 75% of MAx HR Rate which for me at the time was 7:00 pace for 2:20 I Would not go longer, unless I wanted to do time on feet run where I would go 3 hours at whatever pace around forest and enjoy it.
Last 6 weeks very important when possible to go and create workouts that are around Marathon pace.
I also like 3x10k with 2 min rest at 10 seconds slower per mile.
So I would go 35:00-34:45-34:40
I made some mistakes as well. The harder I started to train at marathon pace the worse I got. Need to be relaxed and have correct sensation and that speed. In the race I went by feel and run 2:25 very equally.
Also during last 6 weeks I was unable to PR in the half and can only run 1:12 all out, and then 2 weeks later back to back. So never lose confidence in yourself regardless of workouts. We train to race, so good workouts are just good workouts and nothing more, and bad workouts are same thing. You must forget training each day and move on to the next. Dont worry about small things, just focus on each day.
Hope that was any help!!!
26.2 miles at 5:32 pace