A few tips, the real gameplay expert is sake-bento but I've reached almost all endings myself too:
- the thresold amount that will change the ending with the girls is $1000. If you make more than that, you're successful at farming and you'll stay in Fairbrook. Otherwise you'll get the other endings for each girl
- you rarely need to work for the fullday. if you just work in the morning, you should be able to reach $1000 quite safely
- REST! Since you plan the week in advance, is safe to put 1 day to "Relax". If your health is very high, like >90, you can avoid resting that week, but you need to rest as the first day of the next week
- if your health is low, you'll take a FORCED rest, and this will lower all your stats by a bit
- the first week I believe is best to visit all the girls, then you should focus on the activity releated to that girl, example Jogging to get Clara. However, you still need to alternate a bit and not just do that activity and nothing else
If you still can't figure things out, the first line of each of the girls' walkthroughs will give you the main "secret," and the rest will just tell you the exact choices you need to make to raise affection.