1. Analyse the whole text semantically - make sure you understand what it means. If there are difficult words, these are good examples that your teacher might ask you about.
Make a note of any ambiguities or difficult to understand parts.
2. Break your text into sentences.
Analyse each sentence grammatically (syntactically). That is, work out the parts of speech, etc.
3. In each sentence, find words that are marked morphologically - different from the base word.