‘Always show, not tell,’ is a big fat lie. If you always show, you’ll have half a novel of descriptive words and flowy sentences that will be hard to read.
Here is a quick tip:
Show emotion.
Tell feelings.
Don’t tell us ‘she was sad.’ Show us- ‘Her lip trembled, and her eyes burned as she tried to keep her tears at bay.’
Don’t show us ‘her eyelids were heavy- too heavy. Her limbs could barely function and she couldn’t stop yawning.’ Tell us – ‘she felt tired that morning.’
Showing emotion will bring the reader closer to the characters, to understand their reactions better. But I don’t need to read about how slow she was moving due to tiredness.
Likewise, when you do show, keep it to a max three sentences. Two paragraphs of ‘how she was sad,’ with no dialogue or inner thought is just as boring.