What is the most economical way to use my hot water tank?

i recently bought my first house. new build property with a condenser type boiler and the hot water is pre pre heated and kept in a tank in the loft. i live on my own for now and since i moved in i have been told 2 different things about how to use it as economically as possible. some say just put it on for an hours boost as and when it needs topping up, therefore heating 1 full tank of water each time but only doing so as needed. others say to leave it on all the time so that the boiler instantly just tops up however much how water ive used, so only coming on for a short time but quite often. so i now dont know which is better.. please help!