I is used
1.When one discuss an idea in public which is totally based on his thoughts. EXAMPLE - when a person is delivering a speech he must mention in his speech that I * have some ideas which is based on my pondering towards that topic. So that others don't make your ideas their property.
2.When you commit a mistake and try to have the courage to admit your mistake. EXAMPLE - when a person commit a mistake he should must say "Iam sorry for what I did, instead of putting faults on others."
3.When you don't like what others think about something. EXAMPLE - if someone is saying good about the thing which you doesn't feel that much good and that one decision matters to your family than you must say "sorry to interrupt butI*oppose your point of view" and you must put forward your ideas too.
WE is used
1.When one is working in a group. EXAMPLE- if you are doing a teamwork and got a success you must mention that "We all have done this" and by using word We you can success over any competition.
2.When you are a boss of a company or an incharge having workers under you. EXAMPLE-if a person is a head of any institution he must encourage his workers by saying We can do it.
3.When you are sitting in a family and going to take some important decision. EXAMPLE - if being a member of your family you must take advice of other family members before going to take a big decision which matters to all the family members and should say " We can take a big decision by listening to each membersl views towards that topic.
YOU is used
1.When you praise someone. EXAMPLE -you say in praise of any person that You are so intelligent.
2.When you ask for help from someone. EXAMPLE - if you are in trouble and you think to take help from someone who is not known you than you always used to say that "Can You please help me.
3.When you disagree with what others think about you. EXAMPLE - if one finds other saying wrong about you, you must make them realize that what they are saying is wrong by saying that You are wrong and You should think before speaking against me without any proof.