Yep, the first thing to do is minimise the chances of interference with gas motors.

Start with the ignition system, no matter what the type try to source a shielded plug lead and cap. If you can't do that, as in my case, at least use a quality resistor style plug (eg. NGK R).

Minimise metal to metal contact, particularly from the throttle back to the servo.

Keep the receiver as far from the engine as possible, putting as much material between it as you can. Naturally, route the antenna away from the engine. Be careful not to start overshielding the engine from the receiver/antenna, you could end up with a dead reception spot at certain angles to the plane (eg. head on usually).

If using long servo lead runs buy some ferrite rings and loop the leads around them nearest to the receiver, it does help with the jitters as a friend found out on his plane. At the very least they are cheap insurance and the weight won't kill it either.

After thorough range tests (running and not) and then test fly with FM/PPM receivers. The idea being that if you have any problems they will show up early, giving you the opportunity to minimise interference hopefully prior to first flight. No use starting with QPCM as it may mask potential problems, and if it does that close to fail-safing you will find that out at the worst possible moment...probably take off.

Mostly basic stuff but there were a few things there I didn't know and was lucky enough to implement before I got anywhere near the air.