The clubface has the largest influence over the direction of your shots. A ball struck in the centre of the clubface will leave closer to the direction it is facing rather than the direction it is travelling in.
Curvature in ball flight occurs when there is a difference between where the clubface is aiming and the direction it is travelling at impact (the path). The bigger the difference the bigger the curve.
ANGLE OF APPROACH
Our swing centre is positioned to the side of the ball when we play so our arc of swing should be at an angle of approximately 45 degrees to the ground. Approaching the ball from too far above or below this will cause you to strike too down or up on the ball.
CENTEREDNESS OF STRIKE
When the ball is struck on the toe or heel of the clubface there will be less resistance on the opposing side which will cause it to overtake and miss align the clubface. Heel strikes will will close the clubface and toe strikes will open the clubface.
If all of the above are correct then the faster a club travels at impact, the further the ball will travel however if the above are not correct then there will be a greater curvature in flight.
LEFT TO RIGHT FLIGHT
Right handed golfers that slice their shots have their clubface aimed right (open) to the forward path their clubhead is travelling in (path). The open clubface adds loft, so a well struck shot will fly higher and shorter and causes a golfer to lose up to 40 yards in distance.
The instinct then is for the golfer to swing harder and to the left make their path even further left in an attempt to make up for the lack of distance and straighten their shots out. This combination only makes matters worse as it increases the difference between where the clubface is aiming at impact and the direction it is travelling in (the greater the difference, the greater the curve in flight) plus hitting the ball harder generates more spin and that also means more curve.
If that isn’t enough swinging left also makes the clubhead swing on a steep angle of approach to the ball so a lot of power is being lost their too plus heel strikes come into the equation as the clubhead it in front of it's original address position. Hell strikes will close the clubface so go left.
The family of poor strikes with this swing shape can include: excessive left to right curve particularly with straighter faced clubs, higher/shorter shots with irons, skied shots with drivers and fairways, heavy iron shots, short well struck shots, mishits from the heel and/or toe of the club.