Distinctions in the use of shall and will have broken down, but some careful speakers still observe these principles: (1) Use shall in the first person and will in the second or third person to express future time: "I (we) shall leave soon." "You (he, they) will leave soon." (2) For expressing command or determination, use will in the first person and shall in the second and third: "I will speak, no matter who tries to stop me." "You shall speak (meaning 'You must speak')." (3) To express willingness, promise, or intention, use will (same verb, different meaning) with all personal pronouns: "I will help you now." "You will be a success." Even so accomplished a user of language as Winston Churchill disregarded the basic rules for using shall and will when he declared: "We shall fight on the beaches, we shall fight on the landing grounds, we shall fight in the fields and in the streets, we shall fight in the hills; we shall never surrender."
In general, use should and would according to recommendations for shall and will. Both should and would also have specialized meanings, should in the sense of obligation and would in the sense of habitual action: "You should go now." "He would take a walk every day."
Dictionary of problem words and expressions. Harry Shaw. 1975.