You have get at least one H-scene for every girl apart from Misaki and Claire because you get one from each of them in the intro. Here's what I did:
Day 1
Either 3F or Teacher's Lounge. Don't pick the Toilets because you'll miss out on an H-scene for Day 2. Get an H-scene.
Pick Toilets for an H-scene.
Day 2
Whatever you didn't choose on Day 1, again don't pick Toilets. Get another H-scene.
When prompted with four choices, choose first option.
Infirmary (bottom right choice) and get an H-scene.
During the two choices at home, choose the top option, or you'll get a bad end when Day 3 starts.
Day 3
Choose 3F. You'll be at home for a moment, but you'll be forced back into school.
Choose 1F.
Choose Sports storage.