From the Bentley Manual:
Never use pins or other sharp objects as these will damage the water channels in the jet.
However that is exactly what you must do to DIY. The windshield washer jets look like they might be made of nylon, so they could easily be pierced. Mine hadn't been adjusted in the car's twelve year life and they still moved with even a light touch of my finger. I used a pushpin. A fatter dull needle would be ideal. Dulling the needle or pin on something abrasive like a stone would be safer. You could use the back of the needle if it fits. If the object you use is thick don't press so hard that you might widen or split the jet.
It took me half a dozen attempts before aiming them correctly. If you're not very good at making delicate adjustments and your jets are only slightly off you probably shouldn't even mess with them. Mine went from shooting over the roof to diving at the base of the windshield until I got them reasonably close. You need good eyesight and plenty of light. Place the pin lightly. It should stand on its own when inserted. Fold the wipers up so they aren't in the way. Wait for that last annoying wiper swipe after spraying before readjusting. The problem with the pin is twofold: it's short making fine-tuning more difficult, and it's narrow so there's a lot of play. The jets move so easily that it is difficult to notice when the play has stopped and you are actually moving the jet.
The inner jets should be aimed about 2/3 up the windshield and slightly towards the center. Aim the outer jets not quite halfway up and maybe a fifth of the horizontal distance from the edge.