here's my problem: my tanks always range in the mid-20's because of shorter trips as well as rolling around in the parking lot at school looking for a space. I already try t combine trips so as to avoid shorter errands. What else can I do to improve these areas of my commute?
With parking lots, it's crucial to minimize use of 1st and 2nd and to maximize coasting. The best way is to avoid high-probability-full areas: if you park same time every day then you know where the lot is full and where it ain't. Head toward zones where it's empty, don't try to find the closest spot. (View the walking as an bonus to improve life-span.) At extremes this might even mean parking on city streets fifteen minutes walk from campus, usually where the "neighborhood parking only" signs end. If you must enter a parking lot, do slight blips and coast coast coast. Same when you leave the spot. Train your eyes to scan the whole lot as you approach it, to plan your strategy.
Bike suggestions I agree with too, totally. Be creative. You can perhaps put bike in trunk and drive to within ten minutes of campus. You can carry bike on bus. Etc. Bicycles get you right to the door much quicker than any car. Scooters are another solution. My old one, pictured to the left, got 87 mpg in city riding.