Insert a colon after words that form a complete thought, not after phrases such as for example or as a result.
It is common for someone to write, The topics on the meeting agenda include: the annual conference, staff additions, and budget planning. Similarly, you might see this punctuation: We plan to present the class in: Boston, Chicago, Dallas, and L.A. But no colon, or any punctuation, is necessary in either instance.
A colon should follow an independent clause, one that could stand alone as a sentence. Instead if writing, “For example:” make it, “Here is an example” and then use the colon. Or instead of saying that “Her busy schedule includes:” write that “Her busy schedule includes numerous activities” and then insert the colon and list the activities.
Why colons can create awkwardness
Punctuation is intended to help readers navigate easily, so that they grasp your intended meaning and read the sentence easily without tripping. But a colon often seems to break the thought in midstream. That’s because many verbs take objects, and together, they form a unit. In the sentence, She approved the proposal, the budget, and other resources, the words policy, budget, and resources are objects of the verb approved. When you insert a colon after the verb, it breaks the verb-object unity, and the reader feels as if she is left hanging. Try reading that sentence aloud with and without a colon after approved and notice the difference.
The same is true with prepositions, which are always followed by an object at the end of the prepositional phrase (by the manager, in the conference room). Don’t write that “We could hire her as: a writer, editor, or communications adviser.” Notice that your momentum stops and your voice drops at the word as. Instead, the reader should read fluidly through that sentence without hesitation.