Just a small campaign strategy guide...

This small guide should help you with some campaign strategics. It's not much so far, but should help if you have no idea. Still work in progress, expanded overtime and feel free to add stuff in comments.

Lets begin...

First, this will be a looong playtrough. Rushing the "story" campaign will feed your worst enemy and your worst enemy is the infestation bar. It's not only "Game Over" if it's full, it determinate how hard your times will be. You can't stop it to go up, but slow it down massively and even reduce it often. At the end it will go up, but keeping this low as possible should be your primary goal. To accomplish this, your weapon is "intel", which mean outposts and later "black ops". The point is, Outposts become pricer with every outpost you build (but not upgrading them). But you need them, you want them, cause you need the ressources. Not only supplies for research, building, yadayadyada. Because the most important ressource are not supllies or specialists, it's deployment. So rushing Outposts lvl 2 tech and spreading outposts like crazy is the next point on your priority list. Going "Wide" with lvl 2 outposts is the point where you are going to "rush", not only slow down infestation, but deployment allows you to fly nearly all missions if you time it right and even better, make them easier if you need by setting up mission modifiers. So choose wisely, supplies and region bonus is not everything. Prioritze "high deployment" for many missions and "high infected" regions to reduce and slow down the overall infestation. Next point is specialists, early on they are rare, later you don't know what to do with them. If a research need 3 or 5 days, doesn't matter in the long run, so invest in upgrading your landship whenever you can, it will reduce mostly your costs for research and engineering and unlocks other important stuff like black ops. You want reducing costs (a new marine for 200 or 110 is a difference), which means you can build more outposts faster. Research overall should be not your priority, but don't ignore it completly. Early on research what you need, not what you want.

Next is missions. While secondary missions have nice bonus and benefits, and often you want them cause of ressources or to reduce infestation in the region, don't prioritze them. Focus on rushing your primary and don't risk your mission by crossing all the map cause you want to rescue some civilians. If you can finish a secondary mission on your way to extraction or it is near your primary, fine, do it. But if it wants you to cross all the map, just ignore it. You will do a ton of missions, don't waste your lifetime to finish them all completly or even worse, fail the mission overall cause you get overrun by STROL. Story Missions mostly don't have a time limit of availability, so only do them if their is no mission available and you have enough deployments and your supplies will refill in short time. You don't want spare your lasts deployments for a story mission, while you get 2 or more important emergency infestation missions 1 day later and resuplly is 2 days away...

Move your HQ. If you don't research (which you shouldn't all the time, cause you wanna spare resources to spread out more outposts and wait for upgrades so they become cheap), use them for "scouting" and make contact with new regions. Only moving HQ or build Outpost does that. You want as much contact with Regions, cause STROL is spreading and kill colonys, even if you don't have unlocked them.

So far, good luck.