While the tips here aren't as indepth as you'll find on GameFAQs, I've played FFVII enough times that I do have a few things to say about using Cid. The thing is, every time I go to replay FFVII, I end up using Cid in my party for basically the whole game. I don't even mean to, it just happens. Cloud, Cid, and Vincent are my go-to party after Disc 1; they get shit done. Of course, then Cloud gets his ass dunked in the Lifestream, but whatever.
The thing about using Cid is that if you want to level up your materia quickly, you're going to use him anyway. He and Cloud are the only ones with triple-AP growth weapons, and Cid's Scimitar has linked slots while Cloud's Apocalypse is unlinked. If you're, say, going for the Materia Overlord achievement in the Steam edition (that's the one where you master every single materia in the game; yes I have it, no I don't have a life), then you're gonna need to know how to use Cid.
Which spear you use really depends on where in the game you are. I tend towards the double-AP growth weapons if they're available, since I like my materia mastered as fast as possible, and Cid gets his first one in the City of the Ancients: the Viper Halberd. It's outclassed not long after by the Javelin, found in Gaea's Cliff, and you'll probably end up using that for most of the time until you get the Scimitar at the Underwater Reactor.
If AP growth isn't a concern, then you've got more options. The Dragoon Lance can be found in Wutai if you got the Leviathan scales at the Underwater Reactor, and it's the only weapon Cid has aside from his ultimate weapon with all 8 slots. (Unlinked, but still.) The Grow Lance has better stats, but is obtained so late in the game it's really not worth it. Of course, there's the Flayer, which you can get by scoring 5000 points in the Speed Square on Disc 2... but if you can actually do that then I kind of hate you, because I've always been terrible at the goddamn Speed Square.
The Venus Gospel, Cid's ultimate weapon, does more damage depending on how much MP Cid has. However, since it has zero AP growth (as with all the ultimate weapons), its use is limited.
armor & accessories
Armor is really a matter of personal preference and what you need at the moment. Do you need double-AP growth? Lots of slots? Damage protection? It depends. I personally tend to give Cid the Dragon Armlet (because he's a dragoon and I like themes) for the half-damage and the high number of linked slots. It's available early in the game, as well, which is nice. When you get to the Gelnika, the Escort Guard is a nice upgrade. Of course, you can also never go wrong with the Mystile or the Ziedrich, but the latter suffers from the lack of materia slots.
Accessories, too, are largely a matter of circumstance. Naturally, the Ribbon is ideal, but if you don't have three, then someone's gotta have something else. The Tough Ring in particular is a great boost to Cid's defenses.
Here's where it's even more a matter of opinion, so please remember that this is just what I do, and your mileage may vary.
Cid's magic stats aren't stellar, but he can get the job done if he has to. I tend to give him the Bahamut summons (again, I like the dragon theme) and the big magic like Comet, Contain, and Ultima. The damage tends to be so high that it mitigates Cid's own shortcomings in the magic department. He does tend to need a HP Plus to make up for the decreases from the other materia, and I often give him Magic Plus as well.
The one thing I always find myself doing is giving him Slash-All, along with the Long Range materia. His strength is high enough that it tends to kill weaker enemies, and doesn't have any downside against single enemies. Plus, I mean, the guy's carrying a spear. Of course he can hit you from long range.
The nice thing about this setup is that with Cid's numerous double-AP weapons, along with his triple-AP weapon, it's a breeze to master materia, even difficult ones like summons, without sacrificing his damage-dealing potential.