i'm no expert on DMC4, and somebody will probably come up with a better post then me.
The process is like jump cancelling, you have to find that one spot in each attack through many attempts (or a handy youtube video, check for those) and practice it until it becomes one of your brains automatic responses, like putting your shoes on and getting in the car to go somewhere without even realizing you did anything, full autopilot is the ideal.
i think the forward lock on move (i don't remember what it's called) is fairly easy to do, i remember being able to get it right a decent amount of the time when i played Nero.
if you've learnt how to jump cancel pretend it's that exact process.
also, a controller reconfig may help you, i use default sword and charge but other button set ups may be easier for you to work with, i only just remembered typing this that my dmc3 set-up isn't the default.