Depending on what type you are flying, you may find that it helps if you keep a little throttle in as this will delay the stall when you are rounding out as the aeroplane will decelerate less quickly. This will inevitably make you more likely to float but on the plus side you will have more time to land the plane.
When you round out, try to fly the aeroplane six inches off the ground. As the throttle will be closed or near to closed, you will find that it will land itself.
I realise that other ppruners will probably crucify me for these tips, but they both worked for me, so its not as if they haven't been used successfully.
Also, looking up the runway helps (as already suggested), but you may also want to try glancing out at 45 degrees from your direction of travel as it can really help you judge your height better.