In To Kill a Mockingbird, nearly everything Atticus says speaks of good advice. His honesty is always consistent in his words and actions. He leads and teaches his children by example. So, simply adopting that behavior (speaking and acting according to principles of honesty and integrity) is something Scout, or anyone, would be wise to do.
Given that the title of the book implies that one should not harm an innocent being, there are many pieces of advice Atticus gives the children regarding this theme. One that is a recurring theme is to consider the perspective of others before judging them (if you should judge them at all). Jem learns this in dealing with Mrs. Dubose. Atticus even considers Bob Ewell's perspective. In Chapter 23, Atticus informs Jem why he did not retaliate when Bob spit on him.
So if spitting in my face and threatening me saved Mayella Ewell one extra beating, that’s something I’ll gladly take. He had to take it out on somebody and I’d rather it be me than that houseful of children out there. You understand?
In the end, Scout learns this in terms of considering other people's mindsets but also quite literally in terms of perspective. In the last chapter, having walked Boo home, Scout concludes:
Atticus was right. One time he said you never really know a man until you stand in his shoes and walk around in them. Just standing on the Radley porch was enough.