When painting over paneling, it is important to start off with a good surface. Find any loose areas that may be separating from the walls. Secure those areas with small nails
Fill holes with a wood filler and sand
It may also be appropriate to spackle large areas.
Sand the entire surface with a fine grit sandpaper. Pay special attention to any burs or rough areas.
Wipe down the surface with a degreaser or denatured alcohol.
Prime the paneling with a bonding primer. This will help provide a durable undercoat for the paint.