Brandon Sanderson is a succesful scifi author who is offering numerous lectures of his on line for free. If you can't afford writing courses or there is something else that prevents you from attending one (e.g. your current location) youtube is your friend.

This is a detailed course that teaches you the basic rules on writing. The video above is the first of a specific course that will navigate you through

1. Introduction to types of writers

2. cook vs chef

3. the illusionist writer

4. world building

5. the box

6.  the business of writing

7. character

8. magic systems

9. brandon mull

10. plotting

11. dialogue and agents

12. Q & A

This may be the most detailed of his courses that are available on youtube. There are plenty more for you to discover and enjoy in form of an online course or an audiobook that will help you on your writing. The complete course is about 12 hours of lessons but I know that once you started watching it you will want to watch it till the final moment.