Try the Benjamin Franklin Method. It is how Benjamin Franklin taught himself to write.
Here is some of his exercises:
1, Select a piece of writing that appeals to you. Franklin used his favorite magazine. The Spectator. You can do this with anything that resonates with you.
2. Jot notes on each of the sentences. Read through again and jot short notes on the core thought of each sentence.
3. Let the notes sit for a few days.
4. Reconstruct only using your notes.
5. Compare your article with the original to identify faults. Does it flow as well? Is IT AS BEAUTIFUL AS THE ORIGINAL? WHAT ARE THE ASPECTS THAT STAND OUT? WRITE THESE DOWN AS FOCUS POINTS FOR LATER.
6. REPEAT! REPEAT!