Well one thing you can do is do whatever to keep your engine revs as low as possible. In “polite driving” you can probably get by without ever having to go over 2500. If it is a manual, you can have pretty good control over this.
As far as driving, that’s the best I can come up with.
You can sometimes bump your tire pressure up about 2 lbs higher than the spec to gain a little bit of fuel economy.
You might consider a performance air filter like a K&N to maximize flow.
If you have a OBDII USB cable like I do, you can get a real-time engine load display and you can try it with various accessories turned on and off to see where your biggest draw comes from. On a small engine like that, you could see 15% or more load by having the A/C on.
Anything that is belt driven is stealing power from the engine, if certain parts are old and worn they could be pulling too much on the engine as well.