Make a plan
Prior to posting your content, make a plan. Select your image(s). Resize; ideally a minimum size of 1280 pixels on the longest side. Remember also, files that are too big will take too long to load on some devices.
Write your content
Study your image. Tell its story. Write as much as you feel like. Then once you have exhausted your mind, take a break. Come back to your prose. Re-read it. Edit it. Then post it.
Write an excerpt
Take a sentence or two from your content. Use this to draw the reader in. Make it interesting. Eye-catching. Absorbing. Now add it as your excerpt.
Look at the categories on the site. Decide which one is the most suited to your image(s), and your content.