How to prepare 40% sulfuric acid solution?

Do you mean 40 % w/v, or 40 %v/v? The first means that you have 40 g of H2SO4 per 100ml of solution, while the second means that you have 40 ml of H2SO4 in 100 ml of solution. The concentrations of H2SO4 will be different, because 1ml H2SO4 doesn't weigh 1g.