I have to concur with the others and say that practice, practice (and even more practice) will eventually solve your brushing problems. Your Paasche is a good double-action brush, a little too bulky for my taste, but should do the job--with time. (I've played around with one a few times as part of modeling demos done by my local IPMS chapter.)
As a beginner, have you possibly considered getting a single-action airbrush to get you past these current rough spots? Not only are they cheaper but they're much easier to learn and to keep clean (in my experience). You can get some pretty fine lines with a single-action by playing with the PSI, thinner mix, and paint tip. A friend of mine bought the new Badger 200 NH single-action late last year, and he now swears by it. It's designed to do very fine line work. He's stopped using his old double-action for the time being. (This may be as much a function of the type of subjects he's currently modeling as it is his wanting to play around with his "new toy.")
What do I use? Well, I've been back in this hobby since early 1987. In most instances, I've stuck by my trusty old Binks Wren "B" (medium tip) single action, external mix brush--bought it shortly after getting back in. I love this airbrush, and have mastered it. It's the most comfortable airbrush I've ever used. I also have the Binks Wren "A" model for smaller detail work, but only use it on ocaasion. You can play with the settings on both and get very fine lines. On occasion, I even whip out my ancient (late 60s!) double-action Thayer and Chandler "AA." (It depends on themodeling project.) Luckily, I've been able to find spare parts for these old airbrushes by trolling eBay. I recently found out that Binks still supports the Wren. You can even buy a new one as part of a box set--but thery're not cheap or easy to find unless you shop eBay. (There's only one retail Web source for them according to Binks.)
My point in mentioning the above is that there's no "magic bullet" when it comes to mastering any airbrush. (A simplier single-action brush might possibly help you over the current hump.) All it takes is time, patience, and plenty of practice. It's the hand and eye and not necessarily the airbrush that makes for a good finish.
--Ken