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
--It doesn't matter if you take the keys or not
Praise the book
DAY 2--------------------------------------------------------------------------------------
Map: Go to infirmary, clubhouse, library and music club
Go alone
Do not bet with Alisa
--Lose against Lena at the tournament
Map: Go to the football field
DAY 3--------------------------------------------------------------------------------------
Sorry, but I promised Lena
Okay,I'll come...
Who cares? I better keep on looking for answers
I think I'd rather help the guys with their giant robot engineering
--The next choice doesn't matter
DAY 4--------------------------------------------------------------------------------------
Map: Go to the forest and then to the bus stop
Don't go with Miku
I think you'd look gorgeous in it
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 with Lena
--Choose any combination of directions
Tell her you went alone
DAY 5--------------------------------------------------------------------------------------
Map: Go to infirmary
--Go with Lena if you want the good ending, with Slavya if you want the bad ending
Yep, I tried my best!
Map: Go the infirmary, to the club house and then to the library
Try to snatch the book out of Alisa's hand
Try to find out what Alisa and Lena are arguing about
DAY 6--------------------------------------------------------------------------------------
Map: Go anywhere you want
--Help Alisa if you want the good ending, don't interfere if you want the bad ending