https://twitter.com/SaraSoueidan https://twitter.com/anatudor https://twitter.com/LeaVerou
2. Get a codepen account and start experimenting, sharing new ideas on css forums ect.
3. Try to replicate some css frameworks like pure. Read the code; try to figure out how they did something.
4. Finally, I recommend CSS Secrets book by Lea Verou. You can buy a pre release copy.