There are two types of hour builders. The ones that go and burn holes in the sky and get into bad habits ie: out of trim, off heading etc. Then there are the people who go to their intended CPL/IR school and work out a bit of a programme. Its not difficult to work out which camp is the most sensible to be in.
Make the most of your hour building and it will pay you back in spades. Find out how the school does their plogs & fuel planning. Ask them what the main problems they find with people doing their CPL and correct those bad habits during your hour building. Get a copy of their SOP's and checklists and read through them. Be regimented in your flying and don't accept flying 50ft to high or low or 5 degrees of course. Trim the little bugger so that it flies where you want it to do. Get loads of landing practice in. Do lots of complicated cross country flights and go to challenging fields that require lots of ATC practice. Most of all have fun.