Usually the best combination would be obviously law, and very surprisingly math. Most prestigious universities require math as an entry requirement. But besides that, psychology, economics and literature will really expand your general knowledge and critical thinking skills which is really important towards presenting an argument. Hope this helped!

Try flash cards or relating a certain part of the date to the key event you're trying to remember. Additionally repetition is invaluable - keep rewriting what you remember on a blank piece of paper and mark this against a master copy with all the answers. It'll soon become mechanical to associate the dates and events/data in question.