Character Similarities
Squall's personality is like Cloud's: Cold and Heartless
Tifa and Rinoa are kinda the same because they both have dark brown hair although Rinoa's hair is cut shorter and they also get the main characters. :)
Zell and Barret are like the tough guys in the group.
Zell also swears a lot like Cid in FF7
Random Speculation: Zell's grandparents might be Cloud and Tifa because he has the blond spiked hair like Cloud's and fights like Tifa using gloves. His limit breaks are kinda like Tifa's too, like Dolphin Blow and Final Heaven. Also when you finally go into Zell's room, he says that his Grandfather was in the war and he wanted to be just like him so he joined SeeD. The designers might have based Zell from Tifa. (ya never know)
Irvine and Vincent both use guns as weapons
Does the name Selphie sound a lot like the name Yuffie?
Did you notice that there is a Cid in almost every Final Fantasy, but they're always different.
There is a Biggs and Wedge in Final Fantasy VII, Final Fantasy VIII and Final Fantasy VI. Where's Jesse?
And of course there are always chocobos. Although you can't do as much with chocobos in Final Fantasy VIII than VII. In FFVII you can breed them, race them, and ride them. In FFVIII you can catch them and ride them and solve there puzzles in the forest. In FFVI you can ride them.