When you say it drifts to the left, do you mean all the time, or just during take-off? It is normal for it to drift left when taking off due to rotor downwash and the fact that the tail blades will push it left while trying to keep the heli pointed straight. If it drifts left all the time than most likely the swashplate is not level.
To check the swashplate, first UNPLUG the wires to the motor. Then turn on the Tx and then plug in the battery in the heli to power up the Rx. Next, flip the 'idle-up' switch to the on position and check the swashplate to see if it is level. If it is not level than just pop one of the ball links off at one of the servos and lengthen or shorten the linkage rod until the swash is level.

Most important, make sure that you unplug the wires to the motor first so that the rotor blades won't spin up as they can cause some serious injury if they hit you. Oh, yeah and when checking the swash make sure both sticks are at the mid-stick position..