To be honest I always solder the power jumper blobs on the top and bottom of the board to connect both 5V circuits, so that the Atmel chip and hte OSD chip share power and ground. This is because there has been lots of problems with the minimOSD voltage regulator failing, and you never know. Although this has been improved with newer revisions I still prefer to not use it as you dont want your video feed failing mid flight!.
With the two blobs soldered your OSD will be powered from your flight controller (or via some other 5V input). And then you will only connect the ground and signal wires to your FPV gear, as you FPV gear will run on a separate power system.
Hope that helps, if you need me to label the jumpers you need to solder please let me know.