Resistance Communications should be next, allowing you to activate the resistance in new regions to increase your reach and your income. Completing that will let you build the Proving Grounds, another critical structure. Next, do Alien Biotech, which opens up the Advanced Warfare Center for construction and gives you access to the Officer Autopsy research. There’s a few key things to focus on early: Modular Weaponry research allows you to apply looted upgrades to your guns, increasing their power.
Two of the most important choices you’ll make in XCOM 2 are what to research and build first.