For tyres use correct pressures and make sure the tracking is correct.
For fuel its Gas to go - Brakes to slow. use the correct gear for the speed you need. Dont use 2,3,&4 as a means to get to 5th. The engine is most economical at its torque peak so use the revs as necessary. Changing up too early makes the car go slower and wastes fuel. Of course screaming the revs for no reason isnt good. Just keep it spinning.
Dont use the box to slow down. Slow in your running gear and slot into the correct gear to accelerate away. Using the box to slow down is tough on gears and clutch and not necessary.
Only select 1st at less than 10 mph when 2nd cant pull you away. If stopping dont select 1st at all.
Dont touch the brakes every time you see a hazard. Some drivers do it constantly with brake lights going like a disco. All they do is polish the pads, reduce their stopping power for when they need it and wear the brakes prematurely.
Dont pull away sooo slow (im safe and economical Oh yes) or stop 10 yards short and inch forward. All this does is waste petrol, annoy everyone else and wears out your clutch.
Use the police driving methods. Accelerate quickly (not madly) to your correct speed and make good progress.
When you maintain your speed you will use less fuel and get there quicker. Brake for actual hazards but otherwise avoid using the brakes all they do is turn your expensive speed (and petrol) into heat that you then have to put back again.
On A roads watch the length of visible road ahead. If its getting longer you can accelerate or maintain speed. If its getting shorter (road bend, junction, slow vehicles, etc) slow down. when you see the road opening up again speed back up to your cruise speed. This allows you to safely maintain speed and often you can overtake slower cars even if your car is not very powerful. You are not relying on brute grunt to get by.
On M-ways for every 2x you look ahead look 1x in the mirror(s). Then you can judge overtakes and lane changes with minimal slowing down.