Landing on the numbers may not such as good idea on a grass strip where they have got other enthusiastic cutting the numbers into the turf or filling the 'numbers' with stone chippings which could be interesting!
Otherwise if the runway is long enough land where you want as long as you do it safely, if you dont need to aim for the numbers and try and force it you may cock up! Remember, treat every landing as potential go-around....
My 2p
J.