Doing the right thing is always a good thing, but for me it comes down to a few questions:
+ What do I believe saved me? (Accept / repent / believe)
+ If I do this thing, will it affect where I spend eternity? (No - once saved always saved)
+ If I do NOT do this thing, will it affect where I spend eternity? (again, no, same as before)
+ What is my motivation for doing this thing? (I want to do the right thing and please Christ)
It is a difficult concept. You get saved, and you feel the Holy Spirit within you, prompting you to do the right thing. Then you hear some whispering doubting your true intentions for doing those things - and at this point you should stop.
I needed to say for myself that my doing good things was a direct result of my getting saved and my going to heaven and my wanting to please my Savior; and that doing good things was NOT going to get me into heaven - because I already was headed there because I was saved.
Kind of circular logic, but if you really think about it, what we all said may help make it a little clearer than mud to you.