Flight Assist was borked a long time ago. It's not nearly as useful as it could be. FA Off is like ultra hard mode. Don't bother with it off, IMO.
So, the best position to fire on your target is from behind them. If you can get in behind them, great. That's what they're trying to do to you.
Fight in your Viper since it's easier to get into position and stay in position with it.
Use 2 energy weapons and 2 kinetic weapons. Until you're better at combat, use all 4 gimbal weapons. Like, 2 pulse (not burst) lasers and 2 multi-canons. Shoot shields with energy only, shoot hull with kinetic weapons and use energy weapons when your capacitor can take using both (not sure what your build looks like).
Target drive subsystems.
With all that said, the only way you're going to be able to get behind and stay behind your target is to know where they are and where they're going, right? When you have them targeted, the holographic display of their ship to the left of your radar doesn't just show you a picture of their chassis. It shows you the orientation of their ship to your ship. You can tell which direction their ship is facing, which way they're flying. Combined with their distance, you can now begin to learn when to turn toward them if they pass you or turn away from them to loop the opposite direction.
Jousts are no good unless you're in a tanky ship and are familiar with strafing left/right/up/down while jousting, which is valid but probably not the best thing to try when you're just learning to dogfight.
If a ship is within 1km from your ship, you should be slowing way WAY down. You'll probably end up lower throttle than the blue throttle arc trying to keep them in front of you (like, when their trajectory will take them right past and behind you). If a ship is more than 1km away from you, consider speeding up to full throttle or somewhere between full and optimal turn throttle trying to get them back to that 1km mark.
NPCs are dumb. They don't juke and turn like players do.
Pick your targets, too. Don't jump all over an Anaconda if you're having trouble.

Start small. Find Sidewinders (which you should find plenty of if you're low combat rank).
A good place to start is going to a nav beacon, but I usually skip those because target density is meh. Instead, Use your galaxy map / system map to find a planet with rings. Fly out to that system and to that planet and look for Resource Extraction Sites. It doesn't matter what kind of ring (metal, w/e). Just make sure you're not fighting on the dark side of the planet. Jump into the RES and stay out of the actual rock ring. Fly around above it or below it. If nothing spawns within 5 minutes, then jump back out and find another RES. Most of the time, ships will start spawning within just a minute or so. Keep cycling through them or use your right-side panel (contacts) to search for ships that are wanted. Before long, you should have a steady stream of targets to pummel.