For mod ideas, I'd really suggest sticking to the
65+ mods that we know work, unless you're a real experienced car/engine/aero guy. If one simply implements a handful of these mods you're pretty much guaranteed some decent gains. Note, K&N filters and cold intakes are not on the list. Warm air intakes are however. Exhaust could be, but its quite expensive and probably not worth the cost as you'll never recoup it in gas savings.
If I were you with a new leased car, I'd be looking at:
1) scangauge or similar
2) air up the tires
3) grill block
4) air dam
I'd also start a garage entry and fuel log to track my progress.