If your are in a flat scissors and stalemate there are a couple of things I do:
1: You can try Nose above horizon, this will slow your plane give a bit of alt maybe help to get inside your opponent.
2: Nose below horizon you will speed up and gain a little E, though essentially you are still flat turning,
3: Mix the above up while fighting, one turn above, one below this will hopefully stop you from flying through your opponents sight or he will have to manover to get the shot and could possibly burn more e.
4: going really slow, flaps try to get you opponent to stall.
5: last ditch attempt to get a snapshot, after flaps the old put down your landing gear airbrake trick, you WILL get inside him but if you dont get him you are now very slow, and even if you do kill him your a sitting duck for the LA-7 or niki which will dive in and kill you.
6: the terrain, remember if you are scissoring at low alt you can use the terrain to help you, try to make your opponent fly towards a hill so he has to pull up and burn more e while you can nose low into the valley and gain e. or he will have to break off.
hills save me quite alot these days
most of all know your planes, as its pointless going low and slow with a plane that does it better than you. at which brings me to my last suggestion.
7: hit F12 and ask for help. dont expect it as some guys do actually respect the fact that a good 1v1 is hard to find and will not interfere until asked.