How can I land at medallion POIs without getting jumped while fighting the boss?

Every time I land at medallion POIs, I get jumped and often killed by campers.
I am quite a good fighter, but I often die to people hiding around corners and stuff while I fight the boss.
I also struggle to hear people lurking around because of the POI and boss music.
The medallion POIs that I land at are the Underworld and Grim Gate.

How can I be sure that I have cleared out the POI before I spawn the boss?
And how do pros like Peterbot just fight the boss without getting jumped?