Trust your plan. You'll have points where you feel you've not done enough, or think you should be doing more during your taper but just trust it.
Include hills training and intervals in your training, the difference they make to your running fitness is invaluable.
Mike sure you've tried you kit, nutrition etc a few times before race day. Nothing new on the day!
Don't get carried away at the start, run at your own pace. Try not to 'zig zag' too much if it's crowded at the beginning.
If it's a race with lots of support, pace yourself when it comes to interacting. It's so tempting to High 5 every hand offered but you'll soon get tired! That said, be prepared to take sweets off strangers!
Enjoy it! You may have a race day that goes exactly to plan, you may have a nightmare day, or more likely something in between). Whatever it is it will be an incredible achievement just to get to the start line after months of training, let alone running 26.2 miles.
(Just a thought on the topic of taking painkillers above. It's generally recommended not to take ibuprofen before long distances as it can have a negative effect on kidneys. Think paracetamol is generally thought to be ok).