You definately need to know about events before 1455 as one of the questions usually involves analysing the causes of the break out of conflict in 1455. So here it will be goo to talk about Henry VI's instability but also his personality (especially how he made favourites, therefore Richard, Duke of York being excluded from court). This is important as when York got a taste of power from his two periods of portectorate, because of the times when Henry VI was incapable of ruling, he gained important support from nobles etc. as they were beginning to get tired of Henry's incapability.
Another point to revise would be the role of Margaret of Anjou, especially the Parliament of Devils. She was the one that convinced Henry, York was after the throne, thus increasing the chance of an outbreak of conflict.
The Cade Rebellion is not essential, but it is worth giving a look-over. It could be seen as the first sign of conflict between the Yorkists and Lancastrians.
The best ways to revise for this exam is the write out time-lines and/or make revision cards. You could also do posters on each monarch between 1455-1485, stating the good and bad factors about their reign and why they were defeated/usurped etc. Instability, foreign and financial policy and all of that.
I'm guessing you'll be doing Henry VII as well? What's best for him is revision cards and then notes/posters on his financial policy, foreign policy, nobility and then threats the to throne.
I hope that helps a bit... I've got a retake on Monday and that's what I've been doing so I really do hope that helps!
Good Luck x
No, I think those are the main ones. You don't need to know them in too much detail, just the general gist of how each side stood against each other and then, for example, how the Stanley family gave Henry VII the extra support he needed to win Bosworth.
May is plenty of time; it's good if you're starting to revise now because most of it is trying to remember the key factors
It's okay! Glad I could help! And to be honest, it kind of helped me as well to write it all down xx