おかげさまで is said in response to a compliment, e.g., congratulating you on doing something well - like "wow, you did really well on your test!" To be humble and polite, you say okagesamade to mean "it really was thanks to your help, your good wishes, etc." ありがとうございます　just means "thanks you". Incidentally, while we say "thank you" in response to a compliment on a job well done in English, saying ありがとうございます in Japanese *may* sound conceited (meaning, "yeah, you're right, I did really well on the exam!") So depending on the situation, to be humble, say おかげさまで。Basically, useおかげさまでto be humble and attribute the credit of your good fortune to the speaker...