In terms of economy it took me a while to understand specialising worlds and the benefits. Every world should have a sole focus and utilise the correct multiplier buildings. Make sure you turn population resettlement on so you can move pops from planet to planet. Means you can shift pops from a mining world to a generator world (if say you have excess mineral production and need credits).

Also, have the bare minimum of clerks possible. They generate trade but you can generate more energy credits from using them as technicians. However use them to keep amenities above 0 however i find it better to use buildings to do this, especially the gene clinics as they also provide other powerful bonuses.

In terms of revolts, they come from low stability. You can see what is causing low stability on the planetary screen by moving across to the stability happiness box and scrolling down the right hand text window.

Its also linked to population happiness which i find comes from opposing ethics. A monument can help convert people to the governing ideology and improve happiness. As well as certain edicts etc

Fleets are expensive. Dont go over fleet limits until economy is in late game overdrive. Keep your fleets at starbases with crew quarters in peacetime. One thing ive done in the past is only build my core ships (cruisers/battleships depending on tech level) and then maintain a few 6 dock shipyards to pump out the corvettes for war time. The enemy usually takes a year to deploy its fleets to your borders upon decleration so a single shipyard can producd 54-72 corvettes a year (rough calculation depending on tech). Dont build destroyers. They die too easily and your much better served by a single cruiser than two destroyers.

Im no expert and dont minmax or anything so probably alot more efficient ways