Why didn’t the Death Star just jump in a position where it could immediately fire at Yavin 4, instead of circling the planet for half an hour?
Because it was clearly tracking/following the Millennium Falcon. The film shows the Falcon, having come out of hyperspace, arriving at a big red planet and flying under (around) it to a little blue planet. It makes sense that the DS would follow suit and assess things from there.
Wouldn’t the tracking device show them where exactly the Falcon is in relation to the planet?
My own explanation is that there are certain hyperspace routes, which are safe to travel. Outside of these routes, you can only go under light speed. The DS could only enter Yavin’s orbit at this specific point.
The same thing applies to TLJ. Once the Resistance ships were fleeing, the nearest hyperspace access point was behind them, so the FO couldn’t simply jump ahead.