Since I am very unschooled in the ways of man sex, I think what I know is more at place here.

I have very well played all three KH games so far and have pretty much conquered the world with this spikey haired, heart following, smiley, key wielding little b*****d.

KINGDOM HEARTS Chain of Memories:

Sora's game made easy: Stick with the cards they give you at first for a little while, maybe the first level at most.
Every level/world you go to, use one "Teaming Darkness" card and kill

EVERYTHING in the room, you'll always be in good shape for levels.
As your stack of cards grow your set up should be like this:
--Several 0 cards
--A bunch of attack cards starting with higher numbers and working down to lower numbers. Also, try setting it up so you use the card that hits hardest for that part of the swing, those being "Strike, Thrust, and Finish.
--Cure Cards
--Hi potions

Once a level also use a moogle card and buy a pack of attack cards.

KH2: tips and tricks
If you have a lot of skill, bosses and such should be easy for you already. I've beaten Hard Mode with 100% and low levels(Sephiroth went down at level 39 with the Winnie the Pooh sword). However if you're still having problems:

Easy Leveling: At pride rock get yourself low on health, and go ontop of pride rock, the roof has a ton of yellow flying heartless you can cast magnega on, this effectivly gains you a lot of experience that will boost your levels atleast 8 levels each run and doesn't even take 5 minutes to do.

High Mobility: Take all of your forms and get them to level 5(or 7 if you have Final form); This gives Sora some new abilities to equip which are very useful in beating Sephiroth at any level. To easily level forms you should stay near a portal to whisk yourself out of the world so your drivebar is always at max.

Valor Form: The throne room at the land of dragons, and the hall outside are good and offer you plenty of things with a decent amount of HP to beat the living hell out of.

Master Form: Same place, the big spear centaur heartless drop plenty of form drive orbs, or the weird objects outside also drop a healthy amount.

Wisdom Form: Same place; You get about 20 heartless each run.

Final Form: Yensids Tower, simply glide down, cast thundaga, and everything will quickly die. As you go up in level you'll find it easier to go deeper and deeper down the tower and to the save point at the bottom.

Dual Keyblade wielding; The Battlesystem is simple, its your (strength + Keyblades attack power)- enemies defense) * swing multiplier = Damage. Therefore at max strength(which isn't really max, its possible to get Sora 255 strength and defense). I'm not sure if thats the exact formula, but the (Strength + Keyblade) is true, so Fenrir, unless you need to use as little combos as possible is actually holding you back from doing more damage.

Those damned minigames: Some minigames are best done with the Fenrir, all your combos off and all your negative combos on.

10 second Sephiroth Battle: After mindless hours of material hunting, and maxing out Sora's strength to 255 just for perfection, start the battle by rapidly hitting triangle, then do a combo. YAY!