Antonyms:
General:
* Hot - Cold
* Light - Dark
* Happy - Sad
* Fast - Slow
* Big - Small
* Strong - Weak
* Wet - Dry
* Good - Bad
* Up - Down
* Right - Wrong
More specific:
* Generous - Stingy
* Honest - Dishonest
* Brave - Cowardly
* Quiet - Loud
* Clean - Dirty
* Smooth - Rough
* Sharp - Dull
* Active - Passive
* Open - Closed
* Empty - Full
Gradable Antonyms:
* Hot - Cool - Cold
* Big - Medium - Small
* Fast - Medium - Slow
* Loud - Quiet
* Strong - Weak
Relational Antonyms:
* Teacher - Student
* Buyer - Seller
* Parent - Child
* Husband - Wife
* Doctor - Patient
Antonyms with Specific Contexts:
* Win - Lose (in a game)
* Accept - Reject (an offer)
* Agree - Disagree (with an opinion)
* Push - Pull (an object)
* Enter - Exit (a room)
More Challenging:
* Proactive - Reactive
* Subjective - Objective
* Abstract - Concrete
* Formal - Informal
* Traditional - Modern
These are just a few examples, and there are many more antonyms out there. The best way to learn more is to read widely and pay attention to the words you encounter.