Two Bar Structures
Lots of music nowadays is very heavily orientated on structures that are multiples of two bars. Often themes are presented in an 8 bar form which can be subdivided into two groups of 4 bars which can again be subdivided into two 2 bar groups.
While this form feels very natural for the human ear and many highly popular themes and melodies are written in these structures, you should always be aware to not fall into a too uniform pattern. An 8 bar theme which keeps repeating a two bar phrase more or less exactly for three times is usually not a very pleasing melody.
Also, such melodic structures quickly feel very short breathed. When listening to many really attractive themes and melodies you will see that often even though the external form of 8 bars is kept, the internal structures are more diversified in order to have a longer arcs on the melodic passage.
Using structures that deliberately violate these 2/4/8/16-bar strucutes can feel very interesting due to their unconventional yet relatable form. Such strategies also can be used to confuse the listener when needed.