Completely agree with #2 here - an unfortunate reality of Bud's life is that the truth is often not acceptable and/or would get him into lots of trouble. His position as a foster kid, a dependent who is taken into people's homes makes him naturally untrustworthy in other's opinion, and therefore he has learned the hard way that lying is sometimes the best option, but to do so you need to learn to lie effectively. It is clear that he has learned from experience that the best lies are simple ones and that he is able to remember easily, so if he is further interrogated on his lie he can not be caught out.
"No. 3, If you got to tell a lie, Make sure it's simple and easy to remember."
In Bud's situation, there are times when he has to lie. Most people face it once in a while. The more elaborate a lie is, the more difficult it is to remember all the details. That makes it even harder to keep the lie straight. If you're going to tell a lie, make it short and simple. The more complicated the lie, the harder it is to remember and then be able to pull if off. Most people will not believe you if you stumble trying to remember what lie you made up. Although a detailed lie seems to be more credible, most times short, sweet, and to the point are the best. That is what is meant by rule #3.
In rule #3, which states “If you got to tell a lie, make sure it's simple and easy to remember.” This rule means when telling a lie it is vital to keep it simple so that it can be remembered and you won't contradict yourself later on and therefore show that you have lied. It is this ability that Todd demonstrates to his mother, though as Bud recognizes, it wasn't really a proper test, as Todd's mother was ready to believe anything her son said.