Don't buy the flower when you first meet Aeris.
Talk to Jessie twice on the train home from Sector 8, and tell her
you're "Looking forward to it".
Don't talk to Tifa while she's behind the bar. If you do, decline her
offer for a drink.
Say "...Sorry" when she asks you if you've forgotten your promise.
Ignore Tifa the next morning; don't talk to her, and go straight to
Barret.
Get caught by the Security Lockdown; do not reach the end of the train.
Force Barret and Tifa to jump out early this way.
After defeating Airbuster, before Cloud falls, tell Barret to "Be
strong". XD
When Aeris is fleeing the guards, climb up to the top level and tell her
to Wait each time. Then, push the WRONG barrel. Do this three times.
When Aeris asks if Tifa is your girlfriend, say "Yeah, that's right."
When you get to the playground in Sector 6, tell Aeris that you'll
"Take her home."
Get none of the best items so that Tifa is chosen for the Don's
date. When you meet Aeris, tell her "We gotta help
Tifa!" Or you can have Aeris get chosen and when you meet Tifa tell her "We gotta save Aeris!"
When everyone lands in the sewer, talk to Aeris first. Or if Aeris got chosen, talk to Tifa first.
When Marlene asks you how you feel about Aeris, tell her "I don't
know".
When you first meet Red XIII, tell Tifa to take care of Aeris.
After the battle with HO512, split up into a team of Cloud, Barret and
Red XIII.
When Tifa asks if you can break out, tell her "Kinda hard"
Listen to Red XIII first, Barret second, and Aeris last while you're
in the cell.
When you finally escape Midgar and have to choose your team, pick Cloud, Barret and Red XIII.
In Kalm, after the flashback, tell Barret to "Wait a sec", then
"Is that all?"
Make a party immediately afterwards with Cloud, Aeris and Tifa. In a
house in Kalm, there's a woman who asks you about whether Mako energy is
convenient. Tell her "Yeah, maybe". Talk to the girl upstairs,
and when she asks you if the old life is better, say "No way".
In Fort Condor, disagree twice to the old guy about his plight. After
that, you can go into Fort Condor and agree then, but that's up to you.
Find Yuffie in Junon Forest. Get her into your party. It takes luck, so use any Luck Sources if you got any.
On the Cargo Ship, give Yuffie a tranquilizer. Make sure you bought
one in Junon Town.
On the Cargo Ship, tell Aeris "I dunno..." when she asks about the
Airship.
On the Cargo Ship, when Tifa asks you about war, say "I don't know".
At the Gold Saucer, when you split up, talk to Yuffie first, and take
her with you. Do not choose Aeris and/or Tifa.
When you see Barret again in the Corel Prison, and you're about to go
after Dyne, you will be prompted to make a party. Choose Cloud, Barret, and
Yuffie. Do NOT choose Aeris.
Before entering Gongaga Town, make your party into Cloud, Aeris and
Tifa. Then, when you meet Zack's parents, and Aeris and Tifa leave, ignore
both of them and leave town.
Complete the Wutai subquest, and let Yuffie steal your Materia. After
you get the Materia back, go straight to the Gold Saucer for the date
sequence.