I've been playing for about three years now, and have self-taught myself everything with the aid of sites like this and video elsewhere. Unfortunately, never having had lessons or an instructor my current form for playing guitar has gone unchecked and therefore improper techniques have been encouraged through bad practice. For the past half year I've been trying to go back and re-evaluate what my problems are and attempting to fix them.

A current problem I'm dealing with is accuracy/controlling my picking hand. I have been learning sweeps for a while now, and for the most part I am able to sweep between 3 strings fairly clean. My problem appears when ever I try to sweep more than 3 strings. An example of this is that I can pick all the notes on the up stroke part cleanly but when I try the second half of the pattern going back down using a down stroke motion, my picking hand starts missing strings.
(I apologize if this is not worded clearly enough to comprehend)

Anyways, I was wondering if there are any drills/techniques to enable my picking hand to not miss any strings and enable me to improve accuracy.
I have read and seen that guitarist such as Michael Angelo Batio plants his picking hand so that he doesn't lose track of where his picking hand is on the guitar, but I have also read this is looked down upon by some because it can cause other problems.

If someone could please offer some advice, I would greatly appreciate it.

Again, please let me know if my explanation isn't clear enough, and I can try to revise it to be more specific.

Thanks for your time.
I'm confused to be honest, if you're actually sweeping it should be impossible to miss strings since it's all one motion through the strings in a sweep...

That being said, same rules as usual apply: if you can't do it, you're doing it too quickly so slow down.

Also, no, do not plant your hand on the guitar, you don't need it to keep track of where your hand is and even if you think you do your only real point of reference is where you last picked and which string it was. See the stickied threads for more info.
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Thanks for the response. I think as you mentioned speed is most likely what it all comes down to. Also I've had trouble finding a comfortable playing position where I can be consistent in my movement when it comes to picking, which maybe explains how I am able to miss strings in a single motion if I'm constantly adjusting my right hand. I'll be sure to look over the sticky thread as well as re-read lessons on here for more information. Thank you again for taking the time to respond.