Having chosen your motor, the motor / running gear alignment is very important. In every case the motor to prop shaft or shafts MUST line up perfectly.
Good alignment will mean less load on the motor therefore less current drain and enabling higher speeds. Bad alignment could damage the motor or the speed control putting excessive load on either. The motor and shaft should be in a straight line down through the coupling and prop shaft to the propeller. Use a longer prop shaft and a solid sleeve to check that shafts meet parallel and dead centre. A novice can do a good job if he takes the time to get it right. Always cover with masking tape the motor's vent holes to prevent dust and dirt getting inside the motor when you are working inside the boat, don't forget to remove it before operating the boat.