I can't improve on the advice on the placement of the flashes that Rathdown and others have already provided, but as for the placement of the garter in relation to the top of the hose, it's usually tucked into the fold at the top. This is because if it were any lower it would either slide back up or cut into my ample calves. If I am going very casual - weekend errands and such - i sometimes omit the flashes and just wear the garters to hold the hose up.

Regards,
Rex.