Always check before moving a soldier, make sure he's looking in the right direction, towards bad guys.
To re-select a soldier, press his corresponding icon on the right side of the screen.
While using a shotgun or explosives to open a door makes for a dramatic entrance, using these methods often attracts enemies. Try opening/kicking through the door instead.
It's always a good idea to equip soldiers with health packs before starting a mission. This means you'll be able to heal the wounded.
Avoid leaving soldiers out in the open. Move them to cover as much as possible.
Attack enemies from the rear to catch them off guard.
Although the game gives you the option to break the squad into two-person teams, it's OK to have everyone stick together. Sure, you may not clear the stage in the quickest time, but you'll achieve maximum firepower.
Never throw grenades within range of fellow soldiers. Doing this has deadly consequences.
Spend XP to upgrade a soldier's stats, including Accuracy, Reaction Time, Health, Speed and Evasion.
Make sure each soldier complements the other by mixing the different classes, all of which have signature strengths; the list includes Fire Team Leader, Weapons Sergeant, Breacher, Direct Action, Medic and Intelligence.
The Navy Seals do a great job eliminating hostiles, but don't be afraid to experiment with the other groups. Among them, the Army SF, Army Rangers and JTF2.
Use grenades to flush enemies out from cover.
Better completion times lead to superior mission ratings.
Just like your soldier, automatic rifles have stats too. Spend in-game currency to customize weapons at the Workbench, adding scopes, grips, suppressors and other gadgets that make these guns more effective.