Posted this on GameFAQs and received the below answer from user Fallacia:
The Brady Guide for VIII isn't really as bad for errors as it is for bad advice or just lack of information in general. The main thing to remember is mainly to ignore any advice it gives about spamming GFs or gaining levels to make things easier. That's not to say that you can't get through most of the game with GFs since it is a crutch that most new players rely on until late-game when they start to lose because of it. It's just faster and more efficient to just draw/refine (refine is the earliest source for most good spells via playing cards and card mod) spells to get decent junctions. Not to mention you don't have to go through 30 minutes of summon animations for what would have been 5 minutes with decent junctions.
You also don't have to avoid experience in general, but it's generally counterproductive to go out of your way to power-level since that only makes the enemies have much higher stats since they gain stats a lot faster than your characters do for your own levels. It's not a problem if you keep decent junctions, but it can quickly make things more difficult if your junctions are poor.
The Brady Guide also doesn't fully elaborate on some of the sidequests, leaving some things up to guessing. It does mention most of them and gives some instructions on how to mostly complete them, but some of the information is just lacking.
It also neglects to go into very good details on things like card rule manipulation and more importantly, the traits of the Disc 4 CC should you complete that sidequest before the fourth disc. Without completing that sidequest, refined cards basically become lost forever.
While it does mention the Queen of Cards to some extent, it doesn't really give the best guide on her either. Someone could potentially finish the quest, but a lot of people will keep on losing and winning back cards, wondering why she's not mentioning her father or creating new cards.
There's not really much you can do about it other than reference a guide or just ignore those aspects until another playthrough. It's generally not a good idea to try and do your "complete file" on a first play through of a game anyway, so if you don't feel like sitting by a computer while you play the game or printing out a hundred pages of various walkthroughs, it's generally best to just play to get familiar with the game until you have learned the details that aren't fully explained within the Brady Guide.