The Best method to figure out the correct rotation of a pump is to view the pump as if you were sitting on the motor, or driver, and determine which side the suction is entering the pump. If the suction piping is on the left, you have a left hand rotation pump, Suction pipe is on the right, you have a right hand rotation pump.
In MOST cases with Horizontal split case pumps, the suction flange is larger than the discharge. This may be difficult to see if the pump and piping is completely insulated, so if the pump has gauges, lets hope the discharge gauge reads a higher pressure than the suction gauge when the pump is running.
If the pump is not running, and is insulated, and no gauges are installed your discharge piping SHOULD have a triple duty valve mounted to discharge of the pump, or a isolation valve and a check valve mounted on the discharge piping. This should clue you in when determining rotation because the suction side, in most cases has only a isolation valve and possibly a suction diffuser.