Since the enemies level up as you do, try to keep your level as low as possible for easier battles. As long as your magic is good, defeating your opponents will not be a problem. Draw high level magic when your level is low to increase your status.

Increasing stats:

You can increase all your stats by using GF Eden's Devour ability by eating the following:

Hp: Rinoa in Adel + 10 HP, Ruby Dragon + 10 HP
Str: T-Rexaur + 1 Str
Vit: Adamantoise + 1 Vit
Mag: Behemoth + 1 Mag
Spr: Malboro + 1 Spr
Spd: Pu Pu + 1 Spd
If you eat a Cactuar your health is fully replenished.

The following trick requires Doomtrain, Eden and Tonberry. You also need Doomtrains ability Forbid Med-RF, Edens ability GFAbl Med-RF, and Tonberrys Familiar and Call Shop abilities. You also need to have been to all of Esthers Shops. Go to Esther Pet Shop in the Call Shop ability, then buy either Giant's Rings, Power Wrists, Force Armlets, or Hypno Crowns. Refine them with GFAbl Med-RF into their next form:

10 Giant's Rings to 1 Gaea's Ring
10 Power Wrists to 1 Hyper Wrist
10 Force Armlets to 1 Magic Armlet
10 Hypno Crowns to 1 Royal Crown

Then, use the Forbid Med-RF to turn them into status-ups:

1 Gaea's Ring to 1 HP Up
10 Hyper Wrists to 1 Str Up
10 Magic Armlets to 1 Spr Up
10 Royal Crowns to 1 Mag Up

It takes 150 000 000 gil just to get 100 of the status ups, each. Although this will take a long time, is shorter to do it this way then to eat monsters. You can also Refine Vit Ups by buying Vit-J Scrolls and using the GFAbl Med-RF to Refine 10 into 1 Orihalcan, then Refine 10 of those into 1 Adamantine, then use Forbid Med-RF to turn 5 of those into 1 Vit Up. You also can Refine Spd Ups by fighting a lot of Cactuars on Cactuar Island, and getting 100 Cactus Thorns then Refine them with GFAbl Med-RF to 1 Hundred Needles then Refine that using Forbid Med-RF, into 1 Spd Up.

To get Squall's high HP early, learn Siren's L-Mag-RF before you go to Timber. Get Squall to a high SeeD rank. Answer all the SeeD answers before going to Timber. Walk around the outside of Balamb until you get your pay. Enter Balamb and buy 10 Tents and refine them into 100 Curagas. learn Quezacolt's HP-J ability and equip the 100 Curagea to his HP-J.

Rare card locations:

Alexander
Piet in Lunarside Base.

Angelo
Watts, on Forest Owl's train.

Bahamut
Defeat Bahamut.

Carbuncle
CC Heart.

Cerebrus
Defeat Cerebrus.

Chicobo
Summon four Large Chocobo at all six Forests, then proceed to the Chocobo Shrine.

Debuchocobo
Man sitting on the bench in front of the Balamb Garden Library.

Diablos
Defeat Diablos (Use the Magical Lamp obtained from Cid to find it).

Doomtrain
Timber Pub bartender (Queen of Cards quest).

Edea
Edea at her house.

Eden
Defeat Ultima Weapon.

Fat Chocobo
Man in front of Balamb Library (Queen of Cards Quest).

Gilgamesh
Card Club's King.

Ifrit
Defeat Ifrit in the Fire Cave..

Irvine
Flo, female station master at Fisherman's Horizon (Queen of Cards quest).

Kiros
Man in black suit in Deling shopping area (Queen of Cards quest).

Komoguri
Little boy in a blue shirt running around Balamb Garden's hall.

Laguna
Ellone in Lunarside Base.

Leviathan
CC Joker.

MiniMog
Boy running laps around Balamb Garden.

Minotaur
Defeat Brothers.

Odin
Defeat Odin.

Pandemona
Zell's neighbors; man standing in front of Balamb hotel.

Phoenix
Esthar presidental assistant (Queen of Cards quest).

PuPu
Look for UFOs to pass by during a battle in the following places (you must have Diablos' "Enc-None"):
1. Outside Winhill Town
2. Mandy Beach, northeast of Timber
3. Heath Peninsula, east of Trabia Garden
4. Kashkabald Desert.
After sighting all four, fly the Ragnarok to the rocky cliffs above the Chocobo Shrine. Encounter a UFO and defeat it. Then, head to the crater where Balamb Garden used to be. You will encounter a PuPu. Feed him five elixirs and you will be rewarded. Its only a level 5 card, but is definitely the hardest card to find.

Quezacotl
Fisherman Horizon's male station master (second floor in the station house).

Quistis
"Trepe Fan Club" member #2 in Balamb Garden lecture room.

Rinoa
Lose the Ifrit card to General Caraway in Deling City. It can be won back from Marlene in Fisherman's Horizon.

Secret and Minotaur
Defeat Brothers.

Seifer
Cid at Edea's house; or from Cid on disc 1 immediately before going to Timber on the mission.

Selphie
Selphie's best friend in Trabia Garden.

Shiva
Trade "Girl Next Door" to Zone.

Siren
Card Master on second floor of the Dollet Pub; walk east to battle him.

Squall
Laguna at Esthar Presidential Building.

Ward
Dr. Odine in Esthar.

Zell
Zell's mother in Balamb town.

Find Ko-Chocobo card in Disc 4:

In order to find this card, you must have defeated all the CC group members, the Card King, and have met at least one time with the Card Queen. On the chain in Altemisia's Castle, head to the northern door (nearest to the castle) to return to the world map. There is a Chocobo forest near here. Go and get a Chocobo, then head to the island where you found Edea's home. There is a desert on this island where you will find the Ragnarok. Enter and you will find Shu near the entrance. Start a card game with her after the short dialogue, . Save before playing against her, as she is a difficult opponent.

Find level 6 and 7 Boss Cards:

On Disc 2 in Fisherman's Horizon, immediately after saving Mayor Dobe, when Squall decides to look around by himself, go back to the mayor's house. Go to the right of the house where Squall and Rinoa will sit and talk. Martine will be there. He has a lot of level 6 and 7 Boss Cards. Be careful though, as he is a very good player and has a lot of good cards; He "confiscated all the cards from the students at Galbadia Garden." He will want to play for just one card, though. It will be to your benefit if you can push the rules to be diff.

Card mod list:

1 Geezard = 5 Screw
1 Funguar = 1 M-stone piece
1 Bite Bug = 1 M-stone piece
1 Red Bat = 1 Vampire Fang
4 Blobra = 1 Rune Armlet
1 Gayla = 1 Mystery Fluid
1 Gesper = 1 Blackhole
1 Blood Soul = 1 Zombie Powder
5 Fastitocalon-F = 1 Water Crystal
1 Caterchipillar = 1 Spiderweb
1 Vysage = 1 Wizardstone
1 Cockatrice = 1 Cockatrice Pinion
1 Grat = 1 Magic Stone
1 Buel = 1 Magic Stone
1 Mesmerize = 1 Mesmerize Blade
1 Glacial Eye = 1 Arctic Wind
1 Belhemel = 1 Saw Blade
1 Thrustaevis = 1 Shear Feather
1 Anacondour = 1 Venom Fang
1 Creeps = 1 Coral Fragment
1 Grendel = 1 Dragon Fin
1 Jelleye = 1 Magic Stone
1 Grand Mantis = 1 Sharp Spike
1 Armadodo = 1 Dino Bone
1 Forbidden = 1 Betreyal Sword
1 Tri-Face = 1 Curse Spike
1 Fastitocalon = 1 Water Crystal
1 Snow Lion = 1 North Wind
1 Ochu = 1 Ochu Tentacle
1 SAM08G = 1 Running Fire
1 Death Claw = 1 Sharp Spike
1 Cactuar = 1 Cactus Thorn
1 Tonberry = 1 Chef's Knife
1 Abyss Worm = 1 Windmill
5 Tutrapod = 1 Healing Mail
2 T-Rexaur = 1 Dino Bone
1 Bomb = 1 Bomb Fragment
1 Blitz = 1 Dynamo Stone
1 Wendigo = 1 Steel Orb
5 Torama = 1 Life Ring
1 Imp = 1 Wizard Stone
4 Blue Dragon = 1 Fury Fragment
3 Adamantoise = 1 Turtle Shell
3 Hexadragon = 1 Redfang
3 Iron Giant = 1 Star Fragment
10 Behemoth = 1 Barrier
10 Chimera = 1 Regen Ring
1 Elastoid = 1 Steel Pipe
1 GIM47N = 10 FAST AMmo
4 Malboro = 1 Malboro Tentacle
10 Ruby Dragon = 1 Inferno Fang
10 Elnoyle = 1 Energy Crystal
1 Tonberry King = 1 Chef's Knife
1 Wedge,Biggs = 1 X-Potion
1 Raijin,Fujin = 1 X-Potion
1 Elvoret = 10 Death Stone
1 Quistis = 3 Samantha Souls