Aim Right
A ball above your feet will produce a shot that flies towards the left after contact.  Adjust your alignment so that you aim more towards the right.

Choke Down
Your club will be resting on the ground higher than normal.  Choke down on the club to allow the club head to rest squarely on the ground.

Stand Taller
Compensate for the slope by standing slightly upright.

Flatter Swing Path
A flatter swing path will result in the sole of the club matching the slope and effectively help you with a more solid impact.
(Swinging on a steeper plane will result in the likelihood of digging into the ground.)

Stable Lower Body
For this kind of shot, it is easy to lose control and hit it fat. Keep your spine angle still and try not to put too much power into the shot.

Aim Left
The tendency for ball flight is towards the right.  Compensate this by aiming towards the left of your target. 

Select Extra Club
Select a higher club (e.g. 5 iron instead of 6 iron) as the sliced pattern of the shot will result in some loss of distance.

As there are different severities of uphill and downhill lies, to be sure of the ball position and direction , always take a practice swing to find out where the club is striking the ground. Make an effort to swing along the contour of the ground .
 
If the divot is nearer to your front foot , move the ball forward in the stance . If the divot is towards the back foot , move the ball back in the stance.
 
As the practice swing acts as a rehearsal for the actual shot , this is the most accurate way of determining where the ball should be played in relation to the feet on hilly terrain. Weight transfer will be hampered so the swing will be driven more by the arms. Thus, a slightly shorter grip will help to get a more solid hit.
 
UPHILL LIE : Will increase the loft of the club.
 
DOWNHILL LIE : Will decrease the loft of the club. Take a more lofted club to make sure the ball get up.