Answer:
1. Fish and visitors smell in 3 days. = Visitors who come to stay overnight otherwise end up spending two weeks.
2. Three may keep a secret, if two of them are dead. = People should be careful who they expose their secrets to. The more people they confide in, the less likely it is to stay a secret.
3. Keep your eyes wide open before marriage, half shut afterwards = If someone doesn't keep their eyes wide open, they could miss out on certain opportunities, which could be better than what they have now.
4. Three may keep a secret, if two of them are dead. (this one appears twice; same as no. 2) = People should be careful who they expose their secrets to. The more people they confide in, the less likely it is to stay a secret.
5. When the well's dry, we know the worth of water. = When a certain material object is plentiful it is taken for granted, and we realize the consequences after it runs out.
6. Little strokes fell great oaks'. = When something seems impossible, you should break it down into small parts and take a single step at a time, and you will succeed.