If you need to emphasize a word or a particular fact in a sentence, you can use italics to stress it. That said, italics and other font changes lose their impact if overused. It is best to use such devices sparingly and rely instead on strong writing and strategic word placement to get your point across.
Underlining vs. italics for emphasis
Before the advent of word processing, it was common to underline words to show emphasis. You can still use underlining in your writing and be correct.
Italics, however, are the more current—and more elegant—way to emphasize a word or phrase.
Italics can be useful to emphasize a few words at a time and are especially helpful if only a single word is stressed. But overuse of font changes for emphasis can confuse and overwhelm the reader.
Emphasis through strategic word or clause placement
When your aim is to point the reader toward key facts and phrases, using introductory adverbs and adverb phrases can be very effective. Some examples of these are especially, particularly, most importantly, and above all. Other adverbs work well in the introductory position too. In the examples below, you will see what a difference word position can make in a sentence: The first iteration sounds more casual in tone than the second.
Repetition of a phrase can also have a compelling effect in your writing, rhythmically underscoring the essence of your message.
Another method of emphasis in a series of sentences is the placement of a short, emphatic sentence to punctuate a crucial point and even add an element of drama.
Use with caution: boldface, capitals, and exclamation points
Boldface type can be used sparsely to draw attention to words or short phrases, and is most often seen in business writing. Using boldface for emphasis is not appropriate for academic writing.
“All caps” writing is rarely warranted, and if you use capitals too often, your paragraphs will appear silly and chaotic. In electronic communications, it can even be perceived as shouting.
Some people may actually be offended by the style of the above example. Therefore, use all capitals very sparingly (and never in academic writing).
Similarly, exclamation points certainly have a place in English writing, but they are too often abused. They can be used effectively in fiction and informal writing, but you should avoid them in business and academic writing. Using an exclamation point implies an outcry or extreme excitement and should be reserved for unique circumstances.
A final note about exclamation points: When you do use them, remember that you need only one of them. Not two, not five, not seven. One.