Training for 6s demo as far as gamesense goes should come down to playing it a lot in pugs with decent players, or getting a team to practice with. Over time, you'll start getting into the flow of what to look for at middles, what enemy players you can catch out of position by cutting off their exit route while your scout challenges him, things like that.
For mids, it's about getting damage on certain things to remove their positioning. If you hit a nice meaty sticky on a scout on a high-ground part of mid, he'll likely back off if your team is there to pressure him, which makes winning the mid a lot easier if your team has the right positioning to push into the remaining players on mid.
I've found that the downtime parts of a round (stalemates, pushing last, holding second) can be an opportunity for you to help the flank with a cheeky sticky trap or just general support. The map depends on what you should be doing, but generally you can focus on helping your flank in some way without leaving your pocket out to dry at the chokepoints.