I've got some guitar questions?

Alright so I've been playing electric guitar for just over a year and a half. I've gotten pretty good, I can play some popular solos, I know about music theory, and I have a huge range of what I play, ranging from soft rock to metal to hard rock to acoustic. I do sometimes jam with other musicians and I have some musician friends that have taught me a lot too. BUT Recently, I have hit a stump. I can tell that I'm not getting any better, I'm playing the same stuff I have been playing for the last few months, and when I try to learn harder stuff, I notice that I can't do it very well. People tell me I just need to practice practice practice, but here is where my question comes in, what exactly should I be practicing? Scales? Songs? what?!?! I need to know how to get to the next step! I also really really want to learn how to sweep pick but I'm failing miserably, letting notes ring out and just not doing very well at all. ANY ADVICE FROM A FELLOW MUSICIAN?!?!? (The hardest thing I can play right now is probably One by Metallica, the solo. And some stuff out of Eruption by Van Halen.)