applying contact paper

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The exterior sides of my cabinets appear to be particle board covered with contact paper ( oak design :roll: )
The lower portions on 2 of them are peeling away, probably from just drying out. The third is next to the exterior door, and is the worst. About a foot from the bottom up has suffered rain/moisture damage. My plan is to remove the loose contact paper and recover it. The board underneath is somewhat rough now. Putting the contact paper on it as is not going to work. How do I smooth the rough particle board?
Sandpaper? What grit?
The other two surfaces appear to be smoother, so I will just cut off the loose stuff and recover with new contact paper. Do I need to do any surface prep on them, other than cleaning?
Thanks
ofgift