Your missiles, specifically air to ground types such as the Maverick, tend to behave erratically. Do not fire while near any type of terrain obstruction. When all else fails, enable the "Unlimited Ammo" cheat to avoid frustration.
Avoid always use the default aircraft and Loadout selection. Make sure they make sense before selecting them. For instance, the CPU often suggests the F-14 for a ground-strike mission when the F-18 would be the better choice. Mavericks are recommended at taking out ground targets from a relatively safe distance. Take extras along if you can.
During air to ground attack missions, fly as low as you can starting at least 20 miles from the target. This will make it hard for SAM sites to detect you. When a SAM gets on your tail, wait for it to get about a mile away, then make a very hard turn into its path while releasing flares. Alternately, when the SAM is farther away, hug the terrain and it will likely hit the ground or a mountain peak.