What to do when the steering wheel pulls to the left while driving

Three common faults here are;
1) Steering alignment - if the front tyres are wearing on the insides then the wheels are facing toe-out. If on the outsides then they're toe-in. The only way to really get them aligned properly is by laser light at a garage. Cause can be altered ride height, mounting a kerb badly, wear in suspension.
2) Worn part in the suspension system, most likely a suspension arm bush or ball joint has deteriorated, uneven and/or premature tyre wear suggests this is more likely the cause.
3) Uneven tyre pressures or sizes. If a tyre is down on pressure or one wheel is oddly sized then you can get a diagonal pivot effect accross the car's chassis, causing it to pull to one side.This effect can also happen due to a broken suspension coil/leaf spring for the same reason.