One important aspect is to choose words that resonate with the core emotions of sadness. For instance, the word 'lament'. You can write something like 'He let out a lament for his lost love, the sound echoing through the empty streets.' This not only shows sadness but also gives a sense of the character expressing their pain. Another way is to use words that suggest a lack of positive emotions. For example, 'dull' can be used to describe a character's eyes in a sad story, 'His eyes were dull, reflecting the emptiness within him.' By carefully selecting these types of words, you can effectively convey the sadness in your story.
Use vivid adjectives. For example, 'bleak' can quickly set a sad tone. Just say 'The bleak landscape mirrored his broken heart.'