You have to practice a lot before you will be expert on that...
1. Make sure that the conditions (Airspeed, GS, Wind, Height) are always the same when you enter auto.
2. Pick yourself a "visual aid" you will look at over the front panel.
(in my case i always use a spot i am looking at app.a palmwide above the front panel-giving me an imaginary glide path to follow).
3. Enter auto always with the same speed-if you close throttle fast one time, and slowly another time, it will make a big difference.
4. How do you define your flare altitude/attitude?
Using a radar alt will help-also take a look at the horizon when in the flare...
The rest is just practice.....practice....practice...