I'd generally start with a message saying "hello there!" or something like that. It may be that now they have scanned you they don't want to fight if you have no cargo/bounty etc.
If
they are in a weaker but faster ship and you want to fight then yeah, 4 pips to shields, 2 to weapons blast away and fly backwards trying to keep them centred in your crosshairs.
If
you are in a weaker but faster ship and you want to fight then I'd go 4 pips engines, 2 pips shields and try to get behind them before opening fire. Don't get aggressive whilst they have all their guns facing you
If you are about evenly matched I'd boost at them with 4 pips to shields and start a jousting match. Starting with a burst of shots and a ram attack is generally not a bad start...
As above it really depends on what ships you both have, if you both even want to fight and what you are confident with.
If you don't want to fight you have 2 options. You can boost under them and try to out-run them or you can sit there with 4 pips to shields and activate your FSD (Edit: Or you can boost past and try to stay behind them whilst charging FSD). If you do it whilst not moving they may be confused enough so that they don't start shooting until it's too late and you are gone.
It also shows your intentions are non-hostile so if they don't want to fight they'll generally wait until you are gone and more on. <- I was once followed on my way out of a station by a CMDR who scanned me and had hardpoints out, I flew backwards with my FSD charging so I could watch him/her. They must have decided I was too much trouble since as soon as they saw I was flying backwards keeping an eye they retracted hardpoints and peeled off back towards the station.
In any case sometimes showing you know a bit about what you are doing whilst simultaneously being non-aggressive is enough to put them off. Why fight someone who looks experienced if they plan to leave?