agree with him/her

If you broke up because of an argument or something, and he/she thinks it wont work out, reason with them, even if you dont agree. Just say something like "I completly understand why you broke up with me" or "Yes, our relationship was dull". Dont say stuff like, say you cheated on him/her and you want them back, dont say "Ive changed, I love you, I'll never do it again" because you will appear like your only saying it for you, and not them. If you agree with them by saying "Yes, I was a complete jerk for cheating on you..." then your more than likely to get positive results