I find this mission easy everytime, but that is just me.
what i find works best i head towards the convoy, close to the ground (50m) and fast (300-350km) then keep pressing tab untill the tank at the back is selected (the shilka) and fire a missile. from then it is easy, just press tab fire as DragonFireSg said. If you go after the hind, dont stand still, as you will get shoot at, but keep hgh and on the tail of the hind. shoot with the 30mm. If you go after the su-25 use the 30mm and try and keep up with it, but this is difficult as you dont have the speed, it can be done though. Then just go and land at the base and successe