A good tune up and only run as much octane as is required. That's about it.
Engine designers go to great lengths to laminate the airflow and STOP spinning air in intakes. My 96 Impala SS has a screen in the MAF, a vertical vane in the MAF, and a specifically designed air foil in the TB to stop swirling air, so those tornado devices are a gimmick. Removing or altering those devices has shown either no performance/MPG gain, or even in the negative on this particular car. The magnetic "hydrocarbon modifiers" are snake oil, too.
If you want to take it one more level, try some computer reprogramming. The factory fuel and spark trims are calibrated to provide a very safe detonation buffer and minimize NOx emissions. The result is a slightly rich mixture that is a trade off of HC and CO emissions against detonation tolerance and NOx. Leaning out the mix just a touch will provide a slight power benefit, might save you one or two MPGs and probably put your NOx right at the legal limit.
Don't run thinner oils or use special additives to the fuel or oil. You'll spend more on the additives than you will save in gas and potentially mess things up.
You'll also find that winter blend fuels are much worse in the MPG category. They include alcohol which carries some of its own oxygen. The result is that your O2 sensors richen things up to keep an even mix and you use more fuel.
For now, stick to the regular stuff and wait a while on the snake oil fixes. Get new plugs ($5) check your wires for resistance and arcing (free), check coil and ignition output (free at most chain parts stores) and make sure your tires are properly inflated. (free... or 25 cents at the gas station) Resist the urge to buy special plugs with split tips and multiple anodes. EFI engines' computers are constantly searching for the optimum parameters to the tune of hundreds of times per second. You'd be surprised at how much a consistent spark will be more beneficial than a fancy spark that jumps around. If you want a BETTER spark, use an aftermarket ignition system like Jacobs, MSD, or Mallory and fire it through good quality plugs like NGK or Bosch Platinum. Its an investment that can be made for $120-200 and you can check some Neon forums to see how much fuel others have saved with the ignition boxes. You can usually expect 5% or so.