In a spoiler tag due to length
(SPOILER) Step 1:
Translate all of Future Esthar's theories into a coherent chain of thoughts that can be understandable without even playing FF VIII. Then, a pattern emerges that will result in the appearance of a hidden number when carried out starting with the number of belts that Lulu from FFX wears (this trick was planned by square from the start). This hidden number is the exact time that must be of the in game clock upon scene when Aeris is killed.

Step 2:
Analyze the concepts behind Tetsuya Nomura's character designs. Once one fully understands them, they will see a number that is the hidden theme in all characters. This is the number of Hi Potions that are needed for the revival of Aeris.

Step 3:
Do not trade away the Mythril. Keep it and resist the urge to get Great Gospel.

Step 4:
Aeris must be KOed when completing the temple of the ancients, and her level must exactly match that of the high potions obtained in step 2.

Step 5:
After the party gains control of Cid, feed the fish in the City of the Ancients the Mythril. Because of the playtime at Aeris's death, the fish is actually alive and awake, so he gets out of the way. Go down and where the white materia is you will find an item called &*%^th

Step 6:
When you reobtain Cloud and Tifa, go to the sector five church, and use the &*%^th as well as your high potions on the Aeris ghost. You only have 1 shot at this or you can't ever revive her. This will trigger a boss fight with the Fate Keeper, who has seven times the HP of Penance and can only be damaged by the buster sword. When he is defeted, the &*%^th will vanish and an item called Fateth will be found.

Step 7:
Throw the fateth into the lifestream at Mideel. Aeris will rise from it at level 7 with all limit breaks as well as her true ultimate weapon, the Wisdom of time, complete with master Restore, Barrier, Life, Ultima, Knights of the Round, and full Cure materia.However, her name is also changed from Aeris to Aerith. Even if you named her something else, it will be renamed Aerith. She takes a slot of the party and never leaves again. She also glows because the lifestream is radioactive and glowing Aerith has red eyes. And longer hair. Cloud also decides to dye his hair black for the rest of the game.

Step 8:
The revival scene causes a glitch in the game, so you must then save the game, and on the same memory card as the FF save must have 7 perfect files of Spawn: The Eternal. Failure to do so will result in your Playstation exploding.

Step 9:
Enjoy Aerith. she has a max of 777 HP, 77 MP and is always stuck in your party. Also Sephiroth will cast Traitor on her at the start of the final battle, causing her to constantly heal him, as well as her being immune to all attacks. Defeating Sephiroth will result in a pin up picture of Aeris and Quina as a reward on the The End Screen. You will then be treated to the true ending of FF VII, where a chocobo lays an egg that contains a letter that states that the the Final Villain for the next Villain is none other then Gogo from FF VI. Also it is rumored that it even shows the true identity of Gogo, but this is yet to be confirmed.