Could someone explain to me exactly how the wish spells work. I've played BGII an umpteenth number of times and never tried these spells before. Any advice on how they work, or the best ways to use them would be appreciated. Also, I read that certain choices will result in very bad results depending on which option you choose, and the character's wisdom level.

When you cast wish a djinn appears and you go through a short dialog leading to three possible choices…the choices are not always the same but if you have decent wisdom there is always a good choice.

For best results make sure whoever is casting wish have high wisdom score either naturally or by potion. High wisdom generally means better options and fewer unintended results. If memory serves a wisdom of 16 is adequate for most things.

Of course, having a lower wisdom person cast it is very amusing...
"I wish to summon an army to overrun my enimies" springs to mind.

There are four levels of wisdom in this regard. 18+, 17-15, 14-10 and 9-1.

keep potions of insight at hand to temporarily increase your wisdom if you want to cast the spell.

It's qa great way to finish of Amelisan where you can't sleep between her appearances. You just cast Wish until you get "All of my party has rested and their spells rememorized." Mainly the Heal ones. ;)

Yep. That particular one is soooo cheap since it rememorizes Wish as well. Absolutely no need to sleep unless you are REALLY unlucky and none of your projected images are able to get that option. You can even change the content of your spellbook in mid combat if you dare use the casting time.

What casting time? Improved Alacrity-> wish x5 with a sorcerer. It is a tad bit difficult with mages to pull it off, as it requires a lot of images and that you have your precious level 9 spots filled with a rather useless spell due to its randomness, especially when compared with time stop and improved alacrity, granted a double length timestop and imp alacrity is very likely to come up in 2 castings of wish with 18 wis. Unfortunately, it is just not consistent enough.