Moving the plate will only help if you have a heavy foot. It is only controlling your maximum fuel so if you don't ever get near wot, it won't matter.
The biggest thing that you can do is regulate your speed. Your windage goes as approximately the square of your velocity so it really hurts you to go fast. If you are not in a rush, go 60 or so and you will get great mileage.
There are several things that you can do to your driving style to improve mileage. The biggest one is anticipating. A lot of people accelerate up until the point that they hit the brakes when coming up to a light or stop sign and this is really wasteful. Also, not using wot helps a lot. Since you have a manual, gear selection is also important. A lot of people lug their engines then wonder why they don't get good mileage. This topic has been discussed many times and does make a difference.
As for things to check on your rig, the biggest one is making sure that your tires are properly inflated. Also, removing any unnecessary weight or windage will help. If you want to get real picky, you can make sure that none of your brakes are dragging too.