Here are the choices you need to make in order to get this achievement :
*** Spoiler - click to reveal ***
--The first choice doesn't matter
DAY 1--------------------------------------------------------------------------------------
Do not reply
Run after him
Do not attempt to take the cutlet
--The next choice doesn't matter either
Keep silent
DAY 2--------------------------------------------------------------------------------------
Map: Go to infirmary, clubhouse, library and music club
Go alone
Do not bet with Alisa
--I don't know if you can influence the tournament so...
Map: Go to Genda Square
DAY 3--------------------------------------------------------------------------------------
Fine, wait a minute
You know, Olga asked me to help her tonight...
Who cares? I'd better keep looking for answers
I think I'd rather assist the guys with their giant robot engineering
--The next choice doesn't matter
DAY 4--------------------------------------------------------------------------------------
Map: Go to the forest, then Bus Stop and choose Don't go with Miku
Just asking...
Overdose of stolen candies, right?
Ask about the bundle
Do not give Alisa the activated carbon
--It doesn't matter if you eat the apple or not
Go alone
Keep going right
DAY 5--------------------------------------------------------------------------------------
Map: Go to infirmary
--It doesn't matter with who you go collect the strawberries
Yep, I tried my best!
Map: Go to club house, infirmary and library
Try to snatch the book out of Alisa's hand
Do nothing, just stay seated
Remain seated
DAY 6 & 7---------------------------------------------------------------------------------
--Follow the voice (for the bad ending)
--Don't follow (for the good ending)