How do I run a faster marathon?

First and foremost, big thanks to anyone who’s willing to help with this. It’s a huge blessing to have a space like this and people like you to help along the way.

That said, I’m looking to improve my marathon time. My current PR is 4:08 and I’m planning to run the LA marathon (March 17) in less than 4 hours. I’m also currently following the Pfitzinger training plan and have averaged 40-50mi per week (varied between tempo workouts, sprints, and recovery runs), but I’d eventually like to run a 3:30 maybe by the end of the year?

What do you suggest I add into my weekly regimen to help increase my pace?