How to manage large assembly files while designing ?

Hello all,
As a young entrepreneur I want to know different ways to manage my data while designing ie. Software data and all documentation. I tried several ways to do this but none of the method best fitted so far. Data at the end of most project gets messed up (Which i hate the most i have to spent hours to solve the DATA RIDDLE). I have 4 men team currently and growing. I want lesser time to be spent for this. Please suggest ways/process that you think are best and innovative.