Here you have a video explaining the steps for your description:
1- Introduce the picture (who is the painter? what's the painting name?, when /where was painted?...)
2- Describe the people (clothes, hair, what are they doing?, location in the picture)
3- Describe the place (objects you can see, colours, etc)
Example:
Choose one painting you like, or photograph and write a description.
Decide the vocabulary, the actions, the verbs tenses, prepositions and adjectives to describe people and objects and the place where the action takes place. Don't forget to revise your spelling.
GOOD LUCK!