At this point, the bulk of the training is done. There's not a whole lot you can do to vastly improve your performance on race day by training harder. You probably have your last long run next weekend, and maybe a few more speed and tempo sessions, but the most important thing now is to play it safe, stay healthy, and get to the start line strong, fresh, and ready to make a withdrawal from the many hours you have put into the training bank.
My plan over the next few weeks is to sharpen things up with my race pace, and to work on thing specific to Boston's course. I have a few more Tuesday interval sessions on the schedule, but I'm thinking I may change them up a bit- head to the hills outside of town, jog up, and go down at marathon pace to simulate the feeling of the last 10km of the course- going downhill from Heartbreak Hill to the finish line. I also have a few more of my long Thursday marathon pace runs, and my plan for those is similar- start at or just below race pace for the first 2/3 on the run, make my way to a hilly section, and then hammer the pace on a long downhill.
The thing to keep in mind though is that I'm just doing a variation on the same training I've already been doing- I'm not going to do anything radically different, or try to ratchet up the pace in the hopes that it will carry over to race day, or try to cram in a few more weeks of big mileage. My plan is the sharpen up on the race specifics, and pay extra attention to what my body is telling me. The last thing I want at this point is to do something stupid and hurt myself.
Whether you're doing the Boston Marathon, or some other race, if you're getting close, don't do anything stupid. Play it safe, trust your training, get to the start line rested up and ready to go, and have fun!