Frater RO put up a recent post on Grimoire Assumptions in which he contends that in order to work with Goetic spirits you need to have experienced the Knowledge and Conversation of the Holy Guardian Angel or Baptism of the Holy Spirit or something similar. Read the whole thing - he makes some very good points, even though I don't agree with all of his conclusions.
I posted a picture a while back of a dude parachuting into a pool in a jungle surrounded by crocodiles and labeled it a magician without K&CHGA working Goetia. It was somewhat tongue in cheek. However, there is a spiritual transformation that has to take place in a person before they are ready to be playing with the spirits of the Goetia and getting the kinds of results I and many others receive.
I can say from my own experience that K&C makes grimoire magick and just about any sort of practical magical work much easier to do and far more effective, but where I disagree is that I don't think the best response to this particular fact is to put off the kind of magical work you really want to do until you reach some sort of milestone. If doing Goetic magick is what motivates you to do the work, I say strap on your parachute and jump.
I look at it this way: the preliminary invocations found in most of the grimoires serve to invoke the "bornless spirit" or identify the magician in some way with the divine, so even practical magical work with a grimoire like the Goetia has a theurgic component that will eventually lead you to K&C. RO is right that if you are a beginning magician you should not expect immediate and breathtaking results, but even before you obtain K&C the more you do the better you get. I don't take a lot of the warnings about "stirring up crap" by doing magick that you aren't ready to try very seriously since never in my life have I seen a failed magical operation that did much of anything, horror stories from popular culture notwithstanding. Furthermore, the kind of person who is going to decide that magick is nonsense when his or her first couple of rituals fail is never going to be a serious student anyway, no matter how long they wait.
While it wasn't the Goetia that really called to me when I was starting out, I did encounter similar attitudes about Enochian magick - it was dangerous, I shouldn't do it until I attained K&C, and so forth. As a Taurus I'm stubborn, so I didn't listen and blundered through it, first with Schueler's crummy introductory books and later on with my own ritual forms derived from the Dee diaries. And honestly, I'm glad that I did. Even before K&C I was able to get pretty good magical results and those rituals prepared me well for the HGA invocation when I finally did it. For me K&C proved to be far easier than most of the writings on the subject implied, and I attribute that at least in part to the extensive experience I had already amassed as a practical magician. Rituals change you for the better, whether you are working toward apprehension of mystical realization or conjuring up an extra fifty bucks.
So what are you waiting for? Hop into that circle and conjure something up! You'll be glad that you just did it.