It really isnt that hard if you apply your practice time in a correct way. What you will have to start learning, that is that I dont know where your at with your playing, your gona have to start learning some theory. Learn the scales. Slash plays in a more bluesie mode, so learn some blues scales.

Alot of improvising is involved also.

To play like slash, takes a lot of time, effort, determination. So to want to play like this and to actually play like this, is two completly different things.

It's not hard, just very time consuming.