Before you Play the Kingdom Hearts game, you will definitely want to know these simple but useful tips and tricks. If you have any tips feel free to share with us!
Things to Know Before Playing
Lightning and healing magic is what you want to cast 95% of the time. Put those in the quick-use menu. In the intro one of the FF10 Babies will ask you something about the time. This affects the experience curve. Dawn means you level up quickly early on but slow down later and night is the opposite with noon being in the middle. I don't know which is more effective but you can beat the post game by level 60-75 iirc so choosing Dawn sounds the most effective.
The game asks you when your adventure begins. how you answer determines the exp curve. choose Morning, which makes your "regular content" to-next-levels pretty reasonable. the grind to the superbosses at 99 is even more excruciating, however.
There's a special attack you'll learn as you level up called Strike Raid. this should generally be the only special attack you equip. it's the "core gameplay" special attack that lets you hit distant bosses and knock them out of annoying/dangerous attack patterns. It also gives you some invincibility frames if I remember correctly.
Your choice of weapon at the start of the Prologue (Sword/Shield/Staff) affects a few things like stat growth and how many items/accessories you can equip. The biggest change, however, is that the weapon you choose dictates the order you learn abilities - going with the Shield will let you learn defensive abilities (Second Chance, Lucky Strike) at earlier levels, whereas going with the Staff prioritizes stuff like MP Rage and MP Haste. Because of this - broadly speaking - picking the Shield makes the game slightly easier, while picking the Sword makes it harder.
Magic in this game is one of those things that you need to really focus on if you want to use it well, primarily because the damage/efficiency of your magic is dependent on your maximum MP. If you wanna be a spellcaster, you can, but you need to commit to it from the get-go (pick the Staff, equip MP-boosting accessories and weapons, use MP-related abilities, accept that you're going to be physically weaker and squishier).
There's an option on the Start Menu that at first glance just looks like it sets your spellcasting shortcuts. If you go deeper in, it also lets you set the AI behavior for Donald/Goofy/other party members. There are a few pre-made configurations, but the important detail is that you can set their various priorities yourself so that they don't constantly blow all their MP in the first 10 seconds of every fight and then start chugging their limited supply of potions and ethers.
The game isn't bullshitting you when it says that some keyblades are heavier/harder to deflect than others. If you attack an enemy when they're in mid-swing or blocking, one of you is going to be left wide open while the other gets a free attack in - and if you're using something the game described as lightweight or easily parried, then you're going to be the one stumbling back and getting hit in those situations.
The non-HD remix version of the game has a single missable Trinity Mark late in Halloween Town, in Oogie's Manor.