1. Have excess infantry on sector capitals starting up (especially when not in Law & Order). Secession can happen over night.
2. Create starships sooner. Creating a level 5-6 starship fac for sirius class gunships will net a lot of adamant-type firepower with tolerable speed.
3. Set up 1-2 fully functional post-industrial jumpship bases. A pair of level 10 jumpship bases and autofacs will net about 10-20k worth of space forces every 12-24 hours. This will create a fleet capable of conquering a number of worlds per play session.
4. Save sector capitals first, the rest second. If a sector capital falls, you cannot control planets within its sphere of influence, and many planets will turn over to the side of the conquering empire. Build them up with starships and infantry brigades.
5. Don't add consumer goods to trade worlds. Trade worlds take a large portion of consumer goods, and distribution is hectic and can result in mass shortages. Stick with everything else and you'll do fine.
6. Create exotroop infantry worlds, but only a few. Exotroops take way too many factories in order to create a decent output of them. My recommendation is to make a few of them in a specific corner of your empire, and the rest into armored infantry. You'll need more jump transports though.
7. Get abundant chromium worlds Just get them. You'll use them for a lot of level 8+ goodies.
Will update more until I complete world domination, or if the game is reset.