Everyone on the team should have pinks down at all times- place them in positions that are not normally traversed. Pinks provide TRUE vision - you can see invis enemies with them
They provide a larger area of vision.
If I play mid and we start on bottom of map, I place my vision ward just at the tip of the patch of grass that is behind bluebuff at the spot that touches river. This gives you full vision to their river entrance, and behind the mid lane river entrace - If their jungler was to sweep the mid entrance they wouldnt know it was warded.
If you can get your jungler to place his pink in the mirrored position on their side mid is completely safe from ganks.