Start by leveling the cabinet, then use climatic adjusters to adjust the play surface. A typical shuffleboard has between four to six climatic adjusters fastened underneath, and these can be adjusted by tightening the nuts on the bottom. The methods are slightly different depending on whether the table is concave (table is positioned slightly upward, like an arch or convex (table dips slightly downward, like a valley).
For a concave table, if the dip in the middle is too severe, the distance between the climatic adjusters needs to be decreased, making the table more level. Loosen the two bolts in between the climatic adjusters, then very slowly (a couple turns for each nut) turn the outer two bolts in a clockwise motion. After a couple of days, check the board and repeat the adjustment if necessary.
For a convex table, the process is similar but the instructions are opposite. Loosen the two bolts on the outside of the adjusters, then slowly tighten the inner bolts, pushing the climate adjusters farther apart. As with concave, make sure to adjust very slowly (only a couple turns per bolt) and test the board after a couple days and repeat if necessary.
