It was really much easier when I was in Edinburgh a decade ago and could just see what stuff people had left free tickets for at the hostel. Admittedly, I saw some fairly dreadful stuff that way. Some of that was my own fault. Had I only listened to advice or read reviews I could have entirely avoided Maori drag queens and a woman in a nun costume who talked to stuffed animals.
Unfortunately, some of the least appealing descriptions here involve people I know and whose shows I might, therefore, be semi-obliged to go to.