Do a forum search for Alclad. There are numerous posts describing how to properly apply it and the techniques involved. Basically, the plastic needs to be very clean. Use a good primer and spray the entire aircraft. Once that is completely cured, spray the plane with gloss black. That will create a very smooth surface for your Alclad II. Give that several days to solidly cure. Then spray the alclad. Again, allow it to completely cure before moving forward with decals and the like.
There are much better posts out there with clear instructions. The is also an excellent article on Swanny's website, which you can find here: http://www.swannysmodels.com/Alclad.html
I hope that helps!