Build up your economy in the core first. Consolidate all your fleets and armies into one. Abandon the outer areas until you're really good and want to challenge yourself to hold Eriadu, Kessel, or Bastion.

In space use Gozantis, Lancers, Gladiator Is, and/or Raider Corvettes to support your ISDs. Buy fighter heroes and gain fighter superiority in every fight or die to rebel/black sun bomber spam. Carracks and Strike Cruisers are good against enemy capital ships once you learn how to keep them from dying every battle.

On the ground you can pretty much do whatever you want because of how good the Imperial ground forces are. Darth Vader and Veers are unstoppable (and rescuable) killing machines. Commander Fulik and the airborne hero are also great. TIE striker/fighter spam is crazy powerful.

Garrison every world with either an outpost or (on mining worlds where you want 3 mines+governor's palace) 3 units of army troopers plus 1-2 AT-PTs (great for anti-infantry) and 1 transport I can't remember the name of that buffs vehicle fire rate. This will be more than enough to stop rebel raids.

You can skip space defenses and use only ground forces to defend worlds if you want to delay the enemy/put them at risk of counterattack in space with Hypervelocity Cannon support. Just know that the AI is smart enough to skip these worlds so you'll still have to put a fleet or space defenses behind them.

Golan Is are really good because at higher difficulties the AI will spam 80-100 fighters and bombers with no ships. Their point-defense ability is the only good Golan ability in my opinion. Hypervelocity cannons and Golan II/IIIs are useless against over 50% of every enemy fleet. Large Dockyards are also great because they usually give you a free ISD.

Be aggressive with fleets building up on your borders. The AI will overwhelm you if you don't blow up nearby fleets/stations and keep expanding 100% of the time. You also have to keep up on research. You can't go wrong with blitzing frigates or fighters all the way first but you probably will lose if you go for only capital ships.

As soon as you can afford tier 3 infantry you can raid enemy worlds behind the lines with storm commandos. Garidan is a hero from the Maw questline who helps you see enemy ground defenses.

The Arc Hammer is alright, Bellators are amazing, and Executor SSDs are good but you've probably already won if you're buying the non-hero one.

You will take heavy casualties at first. Being able to rebuild fleets quickly is important. Don't be afraid to crank out dreadnaughts and gozantis in the late game to patch holes in your lines.

Redundant ground and space production buildings are key in the late game to recoup losses quickly. Also, you will need to build population centers and labor camps mid to late game to increase your unit cap.

i personaly love fighter support. gozanti's, dreadnaughts, Gladiators and of course Ton-Falks all give you fighters. later tier will let you construct tie advanced but i say you can safely skip them, even gunboats cuz theres even a Ton-Falk gunboat variant.

imp ground gets some great hover vehicles like tx130s and 2Ms which rock. In space as long as u support ur navy with fighters from carriers or buildable ull be set and u got strong capitals and frigs /crusiers too

As the first guy stated, do just that but also keep buying imperial army troopers like every week. Why do this? Easy its meant to hold planets you take when you expand pretty much every time. Don't bother building space stations it's a heavy waste, build it only when you have a region that is wealthy and secure from rebel or blacksun.

Also for the army troopers, even if you know the attacking force is really huge. Just evacuate them fast, this way you save manpower and when you inevitably retake or take even more planets you'll have a force that can hold down the planet and built up.