Sometimes there are no set rules about clarity: a sentence is simply not clear. The only way to deal with this problem is to practice recognizing it and revising the sentence until it is clear.
What is unclear about the sentence below?
For lunch I ate macaroni I was going to cook the kids for supper.
Don’t try more punctuation! That will only make it worse:
For lunch I ate macaroni; I was going to cook the kids for supper.
Now, it’s truly awful. See what you can do to clarify the meaning of the italicized sentence.