Scared to start Combat Challenges. Any tips?

[CoolMarquis97]

I'm afraid to start the Combat Challenges. I've beaten the campaign and really only need to get 3 medals for all of the challenges before I unlock every achievement. The stealth challenges seem fairly easy but the combat ones looks so difficult. Is there any tips or tricks I should know about them before I attempt them? I can only seem to get 1-2 stars and never that third one.