Our examiner made me put an engine failure checklist on our notice board. Actually, I really like it, so it's stayed up.
Before it goes on to the actions to be taken in the event of an engine failure,
The first lines say:
Prevention.
! Regular maintenance
2. Use approved and inspected fuel
2. Pre-flight checks, including fuel calculation
3. Proper operation in flight, including ensuring tank selection
As you can see, 3 out of the 4 preventative measures (and probably the other one, as well) involve fuel. In the UK, this month's Flyer magazine (other magazines are available) highlights accidents that all involve fuel especially contamination thereof.
The only thing I'd add would be regular, frequent flight operation of the engine. The received wisdom is that Lycoming engines particularly are susceptible to cam shaft corrosion if left for periods without flying. There was a tragic fatal crash of a PA28 Arrow following engine failure a couple of years ago in Eastern England. The aircraft had stood unflown and neglected for a long period.
TOO