At the begining of the game (the very begining now), the two soldiers that get jumped outside the train are both carrying a potion.
To aquire Yuffie you must encounter her in a battle in the forests outside of Junon and defeat her. If you want to figure this part out on your own, then here's a tip: You CANNOT take your eyes off Yuffie, she'll rip you off and you'll have to fight her again. Now, the linking page is a SPOILER, so if you want to figure out how to get her to join your party on your own DO NOT, I repeat, DO NOT read this page for you people who "accidentlly" read too much.
To put Vincent into your party you must solve the puzzle in The Shinra Mansion in Nibelheim. If you don't know what I'm talking about, there's a sheet of paper that you can read in the game that clears all this up. As soon as you enter the mansion there's a room on your left. Go through the doorway and press the X button up against the wall. Cloud will read a paper that mentions the challenge that your about to embark on. Try to figure it out on your own. When you find all the numbers to the safe go and try to enter them correctly. Be warned, there's a sacred monster that guards the safe! Be Careful! I have also moved the rest of this puzzle to another page (has Yuffie on it too).
Don't ever get back attacked again! whenever the enemy gets a back attack on you just tap the R1 and L1 buttons (like you're going to run away) and the characters just turn around to face the enemy never to be bothered by a back attack again.
Near the Gongaga Reator (the one that melted down) there is a monster called the Battle Tank (looks like a Tricreatops with tank treads). If you Morph it it will turn into a Power Source! NOTE: The Battle Tank will not appear outside of the reactor in the forest. You must be on the path that leads to the reactor. Just run up and down right there, you'll run into one eventually.
There is an eaiser way to defeat the Boss Gi-Nattack than fighting him normally. You can use a Pheonix Down on him (remember that they sometimes miss), or if you have an X-Potion or an Elixer then you could use them instead (they hit 100% of the time). The reason why this works is because the Boss is a dead creature, so giving him something that restores life will only hurt him or even kill him.
Ever wanted to get back into Midgar? It is possible to get back into Midgar without using a parachute. Visit the Number 7 gate late in the game and you'll find a man outside who can't seem to find his key. He mentions that he might have dropped it at an excavation site. Well, there's only one of those around, so off you go to Bone Village. Talk to the site foreman at Bone Village and tell him you're looking for "Normal Tresure." Place your hired hands around the top are and set off the blast. they should all point to the location of the "Key to Sector 5." Now you can enter Midgar anytime you want.
By the by, there are some RARE AND VALUABLE ITEMS still left in Midgar, such as Tifa's Ultimate Weapon the Premium Heart and a nifty little accessory called the Sneak Glove, which increases the chance of a successful steal/mug. There is one catch though, the Sneak Glove costs 129,000 Gil. But if you do this late enough in the game, 129,000 Gil is like pocket change. Both of the items are located in Wall Market, the Premium Heart is in the broken vending machine, and the and in the Weapon Shop the owner is the one selling the Sneak Glove.
The General Store in Cosmo Canyon has a backroom that's roped off when the team first arrives. Check back again and the rope has been removed. Now the team has access to the hidden back room and stored back there is an Elixer, Magic Source, and Full Cure Materia.
After Cloud finds himself, visit the basement at the Shinra Mansion (in Nibelheim). Upon entering the library area, you'll flash to a special cinema that explains how Cloud ended up back at Midgar with Zack's sword in his hand and decided to become a mercinary.
If you combine the Cover and Counter Attack Materia in a linked slot, the respective character may coutner attack after after covering for another character.