Tires are too big- Stock size is perfect. It's not a race car.
It depends on where you live, if you drive in B2B traffic etc.
Driving in high gears at low rpm's- You're lugging the engine. The wheels are demanding more power from the engine, resulting in car using more fuel to achieve desired speed. Upshift at 2500 and just coast, try to minimize usage of brakes. When coasting, try to keep engine rpm over 1200- Injectors are turned off at that time ( someone confirm this ). Never coast in Neutral- It's dangerous and engine uses fuel, to keep it Idle.
Use thinner oils- It creates less friction inside the engine.
I keep tire pressure: 34 at the front and 31 at the back. I always try to fill air using Digital air pumps, they tend to be more accurate, rather than analog gauges, with cracked glass and needle jumping up and down.
Enjoy your car! 
My style of changing gears;
1st @ 10
2nd @ 20
3rd @ 35-40
4th @ 55-60
5th @ 75-80
