I've collected lots of tips from the wiki, the forums, and personal experience, and figured the result could prove useful for others. Disclaimer: Some of this advice is copied (sometimes verbatim) from other sources, but I never recorded info to attribute it properly. Suffice it to say that I mainly claim credit for compiling this info, rather than for any single piece in this guide.
The guide is current as of v8.004, with all expansions but Destroyer of Worlds.
So! Here's a somewhat comprehensive list of ways in which you can improve your defenses against general AI shenanigans:
- Keep AI Progress at its lowest possible value throughout the game. Reduce AIP first, expand later.
- Proper planetary defense (turret positioning etc.): Check section 3 of Kahuna's guide here.
- Set up whipping boys: raid warp gates to funnel the AI's aggression (waves, exo waves) to a few chosen chokepoint planets
- The Home Planet yields absurd amounts of Salvage income from waves. So don't make it "safe" until wave sizes get dangerous.
- Advantage of having 2+ whipping boys: it splits up the AI assault. 2x 3k ships > 1x 6k ships. And less AIP loss to gate raiding.
- Reminder for gate raiding: AI Eyes and Warp Gate Guardians also function as warp gates. Check for "hostile wormholes" in the galaxy map (hotkey W).
- Preferentially capture planets adjacent to each other. This makes them somewhat less vulnerable because the defenses don't get immediately disabled once the command station is down.
- Don't alert AI planets of Mk IV-V, e.g. by not colonizing their neighbors, or neutering these systems first (incl wormhole guard posts), or even building a Warp Jammer in the system.
- Neuter neighboring (alerted) planets in general.
- Beachhead neutered neighbors (beware: this alerts their neighbors in turn). In particular, vanguard beachheads in front of whipping boys can weaken a Cross-Planetary Assault before it really begins.
- Give up planets if they've become practically useless after their capture (e.g. those with nothing but ARS, golems, and CSGs) if defending them proves to be more trouble than they're worth.
- Free the Dyson Sphere planet.
- Acquire more defensive power: superweapons (many Golems etc), Core Turret Controllers, Martyrs, Warheads, strong fleet ships, etc.
- Keep Ion Cannons (Mk II+ on diff 10/10) and Orbital Mass Drivers alive on planets you intend to capture.
- Hacking: Corrupt annoying AI ship designs, e.g. those with mine immunity, or with giant range and sniper immunity.
- Research tech to counter AI unlocks (which it gets at the start and whenever its AIP surpasses a tech level threshold), e.g. stuff vs. cloaked ships; defenses with bonuses against common hull types; Counter-Missile Turrets; etc (Best hull damage multipliers according to Kahuna: "I'd say polycrystal>artillery>medium>light.")
- Regularly clear enemy special forces & threat before they become problematic. (One way to do that is to tractor (parts of) them into your defenses: e.g. via Martyrs, Widow Golems, or Riot Starships with tractor modules.)
- Once the Home Planet is secure, build Intra-Galactic Warp Gates so all your ships arrive directly at the front lines.
Responding to imminent waves, CPAs and exo strike forces:
- Place superweapons in strategic locations: Hive Golems, Botnet Golem, SC Martyrs, Lightning or Armored Warheads + Cloaker Starships, SC Attritioner ball; any of these can annihilate all or most normal AI waves of arbitrary size (e.g. 3k Mk II ships)
- Martyrs and Warheads are definitely warranted against the _rare_ exos and CPAs if needed, but too expensive as a counter to normal waves. Also, warheads must be stockpiled and positioned in advance. And some AI ships are immune to area damage, notably Riot Starships and Missile Frigates.
- Botnet & Hive Golem have speed 44. In 1.5 min (normal wave warning time in diff 10), they can travel maybe 2/3 of a hostile system (1-2 wormholes), twice that in friendly systems. Grav Turrets in the attacked system can buy additional time.
- Bring your own fleet back to defend via transports (which have high speeds). (Sufficient defenses make this pretty unnecessary against normal waves.) As a more extreme version, a fleet of SC Jumpships can instantly ferry your starships anywhere.
- Activate the previously built Intra-Galactic Warp Gates in vulnerable systems.
- Build up to the full cap of Area Mines on a threatened planet right after a wave is announced. (Cost: <1 min and ~35k metal, i.e. nothing.)
- Kite threat fleets amassing on hostile AI planets to stop them from attacking.
- Using reclamation ships (e.g. Leech Starships) defensively to dramatically increase your own fleet size.
- Replace an existing Econ Command Station with a Military Command Station in an endangered system. (Caution: loss of energy.)
Responding to AI superweapons (Avenger, Hunter/Killer, Dire Guardian, Golems, etc): check which immunities, hull and damage types they have, then see which of these help:
- ships immune to the target's damage type
- Artillery Golem: can solo many of these, but H/Ks are immune
- SC Implosion Artillery: %-based damage, great range and armor piercing; great vs. H/Ks
- SC Rams and Penetrators (beware: Rams are horrid against the Command-Grade hulls of H/Ks)
- Grav Turrets: to slow the threat if it's not immune
- Special turrets: Orbital Mass Driver (captured or from the Zenith Trader), Heavy Beam Turrets (amazing cap DPS, Radar Dampening), Fortresses (great damage & range; radar dampening)
- Golems in general
- Warheads
- Fleet ball
I hope this will help someone. Feedback is welcome.