Most often it is advantageous to tilt your watercolor board when you paint with watercolors. Even a slight tilt helps the colors mix and mingle. Wet into wet brush strokes magically disappear as you paint if your board is tilted. The angle at which you paint may differ depending upon your own style and comfort. Some people prefer a steep angle and some a simple slight angle. Tilting just the board and not the entire table top is best, then all your equipment, paint, water containers can all sit flat on the table.
A quick and easy way to tilt your watercolor board, simply slide your roll of masking tape underneath the top center edge of your board.