#1
So I've decided I want to learn how to sweep pick, and so I've started to try and learn the solo to `coffin' by black veil brides. My problem is when I try the sweeps I just sound like I'm strumming chord badly. So what is causing this, and where should start in order to be able to sweep well?
#2
Best bet is to look up some videos on Youtube. There are plenty that explain how to get started with the technique. Chris Zoupa has a great video breaking it down. I just started as well and I can actually begin to see my speed pick up. Practice is key.
#3
Sweep picking is hard to learn, and you will need to practice a lot.
I recommend you to watch videos on youtube that explain this technique. The best i know is Ben Eller, his guides are really good, he explains all from the start (+ I find him funny so his guitar lessons are not boring)
Part 1 :
https://www.youtube.com/watch?v=-tob2N4dze8&list=UUcLsvLJOecfCL6RplXhaO4Q
Part 2 :
https://www.youtube.com/watch?v=qm_MA0dpKlY&list=UUcLsvLJOecfCL6RplXhaO4Q

But remember that it will take some time until your sweep picking sound good.
#4
Yes indeed sweeping is one of the hardest tecuniques to lesrn. I would start with 3 notes arpeggios, like the d major shape and d minor shape, they are the easiest ones.
#5
Like all above said, practice is key here. Get a metronome, a simple exercise and only up the tempo if you're playing it flawlessly.

Here are some basic exercises I used. Start with a low tempo that you feel comfortable playing and up 5 BPMs when you're ready. Also check a couple of vids for technique.

http://dl.guitarworld.com/jp_sweep1.gif
http://dl.guitarworld.com/jp_sweep2.gif
http://dl.guitarworld.com/jp_sweep3.gif
http://dl.guitarworld.com/jp_sweep4.gif

These should be enough to keep you entertained for a long time!