Welcome, Sjoerd!
The little Peugeot has a lot of potential.
Make sure you've read the 65+ efficiency mods and 100+ Hypermiling tips (see the page header).
Increase and monitor the tire pressure (make sure you have top quality tires - you'll earn back the premium in lower rolling resistance and better handling).
Keep in the right lane on the highway Speed kills economy, especially with small cars.
Get a partial grill block but monitor air intake temp - I used a cheap in/out digital thermometer with the sensor in the intake until I got an UltraGauge.
Instrumentation like that UltraGauge won't work as unfortunately your car is probably just too old to have an OBDII port, but check out the
MPGuino project.
Most of all, keep a
fuel log. Knowing you're improving is very motivating.
For me, it is a hobby now; one that saves me money to boot.
Cheers, Bart
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2011 Honda Insight + HID, LEDs, tiny PV panel, extra brake pad return springs, neutral wheel alignment, 44/42 PSI (air), PHEV light (inop), tightened wheel nut.
lifetime FE over 0.2 Gigameter or 0.13 Megamile.
For confirmation go to people just like you.
For education go to people unlike yourself.