Build up a squad containing at least 1xSniper, 1xMedic, 1xSapper, 1xMechanic by spending skill points in the appropriate skill (marksman, medicine, explosives, mechanic).Start with few, but capable mercenaries.This will make the looting and the inventory management easier for you! Know your interface: Try every option, try every button, know where every tab is and what it is good for.I prefer Killatomate's 'Realistic Rebalancing mod', but you can also check out this Discussion about those Mods. Realistic Rebalancing Mod v1.8.3 by Killatomate.They make the game so much better! BUT you might not be able to get Steam Achievements.
Use a community mod! They fix a lot of bugs and also add and rebalance weapons and enemies.
