You will need some connections in the crime world to get everything necessary. First, you need a hideout, somewhere the cops won't look for you/find you. Then, you need the right equipment like presses to print the money. You also need original money to check for potential diffrences. Finally, you need a bunch of goons to operate and protect it.
Once you have all that, try printing 1 note of each value, check for differences and improve. Doing this about 5-10 times is preferrable. Once it's (nearly) perfect, you can start the presses at full power. When paying large sums of cash, it is advized to still add normal money. In the traditional "packs" of note money, make the middle, top and botom notes real (about 30-40%), and the rest with your printed money (60-70%).