Bar by bar by bar.
Remember, take it slow enough to get it right and let the speed come all by itself. Practice doesn't make perfect; practice makes habit. It's good technique that makes perfect. Work on doing everything perfectly, no matter how slowly you have to go to do that, and let the speed happen by itself with time.
And as Biff said, start simple. Add the fancy little riffs and flourishes later, when you have the basics of the song down.
I hope this is helpful. Performing even one song well can take an awful lot of work, but it's very gratifying to work at something and work at something and finally, through effort and discipline, succeed.