I've got around 200 hours but I'm a member of a club and fly different types of aircraft. There's only one type that I'm fairly consistent in greasing it on in. The others - depends on the day. As long as the main wheels touch first and the aircraft centerline is aligned with the runway centerline, I guess that's about all you can hope for.
As others have said, it's the sight picture. There are minute visual cues to judge how high you are, but these cues are different for each aircraft type, and sometimes for individual aircraft as well.
What I personally found particularly challenging was going from SEP aircraft to gliders and vice versa. In a glider you sit half as low to the ground as in a SEP aircraft. In fact, you feel like your bum is beneath the surface level.
And at the other end of the scale: I have a mate who is a 737 captain and also flies a Europa from a grass airstrip. Last weekend he landed his Europa for the first time at a major airport with a big runway, and flared at about 20 feet above the runway... Thank god for stall warners and quick reflexes...