From what I remember, stealing is simply dependent on the level ratio of the Thief/Victim, and the rarity of the item. Each mob has its own steal table (most with only 1 item), and those items have a set base chance to be stolen. So increased Dex will not increase the chance, and being blinded won't reduce it. It's all luck.

Good Items to Steal early on:

Hardedge from Soldier 3rds in Shinra Building

Carbon Bangles from Moth Slashers in Shinra Building. You encounter them quite a bit in the room with the model of Midgar, and the Carbon Bangle is great armor at that point. Well worth nabbing for your entire team.

Striking Staff from Eligor in train graveyard. You'll have to wait around for him to show up, but then you can steal the staff fairly easily, and this staff will serve Aeris pretty much for the rest of the game.

Atomic Scissors from those lovely little Custom Sweepers outside Kalm. You know, the ones you get Matra Magic from.

Grand Glove from the enemies that are swinging wrecking balls in the Mithril Mines (don't remember their names).

Boomerang from the Birds in the same forests you get Yuffie in. Much better than her starter weapon.

Most bosses don't have any items up for theft, but the few that do are definitely worth stealing. Remember that stealing from an enemy means that it won't drop anything (for the bosses with steal loot, it doesn't matter, because they either don't drop loot, or their loot is vastly inferior to their stolen stuff [ie: Ziedrich versus an Elixir]).