What are the most effective highway fuel economy tips for high-mileage driving?

[JohnFS]

I drive a lot for my sales job, covering about a thousand highway miles a week in a late-model sedan, and with gas prices being so volatile, I'm trying to maximize my fuel economy to reduce costs. I already practice basic habits like keeping my tires properly inflated and avoiding aggressive acceleration, but I feel like I'm missing some more advanced techniques. For other high-mileage drivers, what are your most effective fuel economy tips for sustained highway driving? Does using cruise control at a slightly lower speed make a significant difference, and is there an optimal range? How much does reducing aerodynamic drag by removing roof racks or keeping windows up actually help, and are there any lesser-known maintenance items, like specific oil viscosity or air filter condition, that have a measurable impact on MPG for a well-maintained car?