Everyone has a different method. Heres how I learn to land at the beginning.
The flare height ranges from 20-40ft depends on weight, or you can fixed the flare height at let say 30ft but change the rate of flare due to weight difference to achieve the same result. If you wanna practice how to land the airplane, I reckon the best thing to do is to learn from the AP first, than once you gain more experience you will be able to fine tune it.
Perform an Autoland in NIL wind condition. From 1000ft use a mouse cursor to pin point your runway aiming point, which is almost always the 2nd set of rwy markings from the rwy threshold (~1000ft from the threshold), so with FAA marking that will be the around touch down zone marking, and in ICAO marking, the aim point would be the one just before the touch down zone marking, or if unsure, it should just be abeam where the PAPI is.
The idea of keeping a constant aiming point is, if you don't flare at all, you should be able to crash into it.
When the AP flare during an autoland, keep the cursor at the same place on your screen and observe how the aim point changes from the 2nd set of the marking to between 3rd and the 4th markings from the rwy threshold. And also the rate of pitch change the AP make for the flare.
Now just try to replicate the same thing manually with the A/T first, if successful your touch down point will always be within 1000-2000ft from the threshold with an adequate rate of descend. Remember, once the Thrust goes to idle at 20ft and the airspeed begins to decrease you will need to pull back slightly to hold the pitch attitude constant in order to reach your new aim point.
However, don't try to make a soft touch down by keep pulling the nose up, with the 773 it's very easy to get a tail strike.
Once you can achieve a safe landing consistently, try to reduce the visbility down to CAT I minima which is 550M. You will find that you can still be able to judge your flare and touch down point quite accurately while not being able to see very far down the rwy. Once you become more comfortable, you may further reduce it down to CATII minima which is 350M and have a go.