I've kept a dream journal specifically for PLL in case I ended up predicting anything down the line. It started happening so frequently that I would sometimes turn to those dreams for theorizing.
My earliest ones almost always involved Mona... For whatever reason, she was dead set as my "A" suspect, and only gave me second thoughts during certain scenes with Alison and Paige.
My first deam that I can remember apparently happened the day before the premiere of the very first mid-season finale. I had seen the promo and the Camp Mona sneak peek by then, so the dream was of the 4 PLLs at Camp Mona, where the night was pitch black. "A" started to speak to them for the first time by using a voice changing program, but the PLLs were stunned into silence because they could still detect Mona's voice through it and knew it was her.
I also had a dream of Mona slowly rowing down a lake or sewer of some kind while an eerie green tint fell over her. She was wearing all black, black gloves, and a hood... and her expression seemed blank and hypnotically... unblinking as she was absent-mindedly rowing. I think this was around the time that season 2 was airing... Then years later, I get serious deja vu from the glowing green Mona doll replacing the Jesus statue and the unblinking Mona in "A's" trunk! I got mild deja vu AGAIN when Spencer made that comment about Leslie Stone "crossing the river styx."
One more memorable dream was a day before the premiere of 2B, and it literally had me predicting "The Eye of the Beholder".
"Inside of what was possibly Alison’s garage, in the dark was the famed video of her talking with Ian on the night of her disappearance, and the Liars were standing still, watching it. However, out of nowhere, Jenna comes into view outside with a clip of some sort attached to the bridge of her sunglasses. Jenna eventually realized something was there, removed it from her sunglasses, and could immediately tell that the clip was actually a makeshift torch lighter. She panicked and tossed it aside as it ignited the yard into flames. The Liars met up with Jenna, who was apparently able to see all along… Could it be that the psychotic A had attached that deadly, disguised weapon to Jenna’s glasses, and that Jenna and the Liars were now working together? It’s unknown, because the dream ended there… But out of speculation, my own logic is surely fitting with the beginning of something I imagined myself, and I thought that A had met up with Jenna, only to betray her in a cruel and sadistic attempt at setting her on fire with the lighter attached to her glasses… This is also an allusion to the night Jenna was blinded, where Alison used the lighter to light the firework/stink bomb and blinded Jenna with the flash… Jenna had clearly received the successful surgery to her eyes, and A BRUTALLY attempted to repeat the traumatizing event his/herself. Could Alison actually be A?!"
Several episodes later, I discover that Jenna gets her eye surgery, and that "A" literally traps her in the burning DiLaurentis house. A few scenes later, it's revealed that Jenna's surgery was a success. I swear to god, I'm not making this up. It's why I write all these down and go to such lengths to interpret them.
My most recent dream was of Ezra being A.D. much like Pretty Little Bee said. He was in the same camp for troubled boys as Lucas and Charles, and so were Bethany and her "twin" Sara (whose real name was Brittney). Ezra was infatuated with the girls and nursed an overpowering desire to control everything and everyone in his life. Aria realized it was him when Ezra accidentally showed Aria a form for their wedding that involved a company A.D. had been known to work with. That's when we see Ezra's whole world unravel as he recalls the origins of how he became A.D. It was like the perfect Ezra is A.D. scenario. XD