Answer:
Depending on what you are writing, I'd suggest using "Domain Specific words". These types of words are words that fit into a certain subject. For example, if you're writing about English, you could say things like "theme", "symbolism", etc.. Though, domain specific words are more so for sounding professional. To actually add words, try and slip in some transition words, which are words like "meanwhile", "thus", "due to", "afterward". Some other words you can add are describing words, also known as adjectives. So maybe if you're describing an animal, add words like "sharp" to describe claws, and things like that. There are many other things you can add, which just revise your paragraph and look at where it seems you can add words and maybe fix up your wording. If you'd like to tell me a bit about what you're writing, I can help you out better. ^^