For xcom2 you need to immediately research the upgraded weapons as soon as you begin your campaign. It feels counter intuitive because it takes so long but it really puts you into the correct pace. I don't remember when it best to upgrade them again or armor but that's the best start. Also aggressively use grenades because they're guaranteed hits.

For BG3, be sad there is no overwatch, sorry, I mean readied action like in D&D.