Picking - is when small areas of coating are pulled off the surface of the sheet. A quick test to see if paper is prone to picking is to take a piece of masking tape and lay it on the paper. Don't rub, just let it self adhere. Then rapidly pull the tape off. Examine the tape to see if there are bits of paper coating on the tape. If so, it is prone to picking.

Ink is too tacky
Adjust or replace ink.
Ink is drying on the rollers
Don't use additional dryers. Check conductivity. Increase ink film thickness.
Paper is too weak / poor paper coating
Reduce ink, or replace paper.
Blanket surface has become tacky
Change blanket.
Ink is drying too fast (multi-unit press)
Adjust ink.