Basically this rules states that a sentence must have a subject, tense, and a verb phrase. What phrase structure rules were used to form the following sentences The boy in the room like puppies with collars. The girl thinks that the boy in the room likes her. Jodi's five handy-dandy tips to being a good tree diagrammer. Your tree represents a hierarchy.
Sentence represents the top of that hierarchy.
Also a phrase is higher in that hierarchy than the complement within it. For that reason your trees must be drawn upward. Again your tree represents a hierarchy and shows the dependency between phrases and their complements. Make sure that the complements are branching off of the the phrases that they are complements of. Draw your trees from right to left.