Choosing the correct preposition to use can be tricky. Idiomatic expressions in the English language use particular words simply because that is the word we have chosen to use. Idiomatic expressions just need to be memorized Other examples are: Capable of Preoccupied with Hesitate in/hesitate to (either is correct) Tied in with These expressions need the correct expression, so it is not grammatically correct to say "able of" or "tied in on" etc.

The uses of the prepositions and examples: On 1. Touching the surface of: on the table; on the wall 2. A certain day: That happened on Sunday, on the 6th of June. 3. A certain street: on South Street 4. About: a book on engineering 5. A state or condition: on strike; on fire; on holiday 6. By means of: live on a pension; shown on television In 1. Place thought of as an area: in London; in Europe 2. Within a location: in the room; in the building 3. Large units of time: That happened in March, in 1992. 4. Within a certain time: I will return in an hour. 5. By means of: write in pencil; speak in English 6. Condition: in doubt; in a hurry; in secret 7. A member of: He is in the orchestra; in the navy 8. Wearing: the boy in the blue shirt 9. With reference to: lacking in ideas; rich in oil With 1. Accompanying: He came with her; I have my keys with me. 2. Having; containing: Here is a book with a map of the island. 3. By means of; using: I repaired the shoes with glue. 4. Manner: with pleasure; with ease; with difficulty 5. Because of: We were paralyzed with fear. Hope that helps. Regards, Teacher Anthony

Anthony does a great job showing us when these words should be chose. I would like to add that there are times when either can be chosen. After you have studied the differences, if you are not sure which is correct, that may mean you have a choice. The language can be forgiving like that. Let me show you: Your own example "in cooking"... Nobody would notice if you said "with cooking." It sounds ok. And in time, you will know what "sounds" ok, if you hear English speakers enough, and this will be easier. You are getting it already. Your three examples are correct. I Want to do better with with my homework. I want to do better on my homework. Sometimes the sentens meaning will change though... I spend to much time on you = I do thing for you to often I spend to much time with you = I do not want to see you this much Both considered correct- just different

I think example 3:We need to spend more advertising.