Best thing is to go slow and use the Vikhr's range to take out any AAA/SAM emplacements you can find. However, in some missions you'll come up against SAMs you can't outrange so you have to use terrain to your advantage and execute a pop-up attack quickly enough to kill it and then drop down before any missiles it launched can hit.
Single MANPADs hidden in forests can be a pain in the rear as well. Only decent strategy sometimes is to fly high and slow and let them shoot at you (so you know where they are), dump flares and run and then engage them from the edge of your range.
General tips:
Most SAMs cannot outrange you, but will fire within about 6km so you have to spot them before they're in range. The ones that do out range you are extremely deadly. If you get a laser ping that you didn't expect (IFVs shooting TOWs for instance). Then dive and turn for the nearest terrain because a SAM is probably ranging you for a shot or is actively guiding a missile.
Most IFVs will open fire under 5km. TOW missiles are easy to dodge though, just generate enough lateral speed that the missile cannot track (usually about 50kph perpendicular to the missile's flight is enough). IFV guns can be devastating, so never fly head-on into an IFV at an altitude where its turret can traverse upward to you.
Tanks will fire under 2km. You should never get this close to a tank, there simply is no reason. The 12.7mm or .50 cals on these things are bad enough, and then there's the main cannon which will knock you out in one hit.
Rifle-equipped infantry will fire about 1km. Usually not an issue, but they can get a lucky hit on critical systems, so don't risk it. Stay away and use the cannon to make quick work of infantry.