English is a complicated language and many of our words have several meanings or usages. However, a good rule of thumb (a rule) is the following. Would is something that is desirable or wishful, or used to describe something that might have happened in the past, or something that is routine. - I would like an ice cream (desirable) - Mary would have invited you if she'd known you weren't working (past) - He would answer the phone if it rings (routine) Should is used to express an opinion or something that is obligatory. It can also be used to talk about something that might have happened in the past. - You should rest after that experience (opinion) - I should do my homework (obligation) - We should have stopped for lunch (past)

Would is a verb 1. past of will, in various senses. Example: "he said he would be away for a couple of days" 2.(expressing the conditional mood) indicating the consequence of an imagined event or situation. Example "he would lose his job if he were identified" Should is an auxiliary verb 1.simple past tense of shall. 2.(used to express condition): Example:Were he to arrive, I should be pleased. 3.must; ought (used to indicate duty, propriety, or expediency): Example: You should not do that. 4.would (used to make a statement less direct or blunt): Example: I should think you would apologize.

There are many usages of these words and many pages of grammar books devoted to these topics. It would be better if you told us what you know so far about these words and wrote some sample sentences. Then we can see more specifically how you need to improve.