nice lol I'm gonna max everything first before going to trip anyway im making a list of event I encountered so far in case any new player is confused(and note for future me) if this not really helping maybe i will delete it.
1. just talk up your sister for the first 10 day, try asking more from her and if she doesn't want to reset the day and choose the other option to increase her "affection", buy her some food from time to time.
2. you will unlock part time and if you don't want to cheat, I suggest you spam the part time job as much as possible since you gonna need money for several thing in game and it also increase your stat which correspond to your sexy time
3. play the arcade if you have the money, still not sure what the requirement beating it but the dexterity is nice to get
4. every morning if there any new thing the sister will tell you one thing per morning so be patient since unlocking many things take several day
5. you will unlock the shrine and if you have surplus of money you can donate to increase your stat
6. when you can visit the school, classroom and the infirmary will be locked you can find the key in back alley and mountain road by talking to your sister. after that explore the school and you will find something nice
7. after you able to do the deed with your sister, it will take a while to open her holes (i don't know better way to saying this) just do foreplay like any normal human would and maybe use the rotor you found in the road
8. you can check the vacant lot after able to have sex with your sister and find porn magazine, a bit of rng but at the end of reading your sister will offer to do the thing in magazine