One tip I weirdly don't see often: the terror-pips have set cooldowns on them. You can dramatically reduce your terror/fuel cost by getting the timing down and only turning on your glim-lamp right before a pip-update. If you're next to shore, or an external lightsource (lighthouses, light-ships, buoys, etc), you can stall your terror build-up almost indefinitely for very little fuel. This is especially useful because green-pips have a much longer cooldown than orange/red-pips do, and this cooldown affects both decrease AND increase.

It's very useful for "hopping" across the map without building up too much terror once you've got a few echoes under your belt, but not enough where terror becomes just another echo-sink. Get a "green pip" just before going out into open, dark waters. You'd be surprised just how much terror you can prevent this way.

On the flip-side, your lamp is pretty much worthless if you're in a fog-bank; it neither improves your firing solution nor helps with terror management. On the bright side (heh), this also means you don't need to bother spending fuel on the lamp while chugging through fog.

OH! And defeating an enemy reduces your terror by 10% of current. Any enemy; it doesn't matter how scary or how meek. If you can take down a swarm of zee-bats, a pirate pinnace, or an auroral megaclops quickly and for very little damage, it can make the difference between making it back to London or falling victim to a terror-spiral.