Money
Spend money to always upgrade your gun in order to qualify for upcoming missions. Completing the missions more efficiently rewards you with more money. The soldiers that defend your base also generate gold, the game's premium currency. The higher level of those soldiers, the more gold they will bring in. However, they also require gold in order to be upgraded. However, this is worth it over time, as you will eventually recoup the cost of their upgrades. Remember to collect gold from them regularly, as there is a limit that they will hold. Play daily to earn rewards that can include gold.
Shooting
Before firing, use the time that you are undetected to take note of your surroundings. Find all available targets and decide which to take out first. During sniper missions, you can use the thermal scanner to find human targets easier. However the time that the scanner can be used is limited, indicated by the gauge that is visible below it. The gauge will refill before the next mission. Consider zooming out fully first before turning on the thermal scanner in order to get the best view of hidden targets, then turn it off.
