If God has delivered you from something, like a wrong belief or an addiction or some area in your faith, do not fall back into that same thing. Even if you are tempted to, pray and ask for strength and tell yourself God has delivered you.
An area for me is finances. God has shown me over and over again that He is the Great Provider. Often I have no clue how He is going to provide, how I am going to make the finances work in our home. But He has shown me that He will provide if I believe no matter what. It is sin for me to doubt. It is sin for me to worry and fret over finances.
Once God shows you something and you fall back into worry, that is sin.