1. Use a capital letter for the personal pronoun 'I'.
Ex : What can I say?

2. Use a capital letter to begin a sentence or to begin speech.
Ex : The man arrived / He sat down.

3. Use capital letters for many abbreviations and acronyms.
Ex : G.M.T. or GMT (Greenwich Mean Time) / N.A.T.O. or NATO (North Atlantic Treaty Organization)

4. Use a capital letter for days of the week, months of the year, holidays.
Ex : Monday, Tuesday / January, February / Christmas, Holi