"trading, gambling, hunting giveaway and signature campaign"

1. Trading is the most good way to earn bitcoin just it's capital needed
2. i don't think gamble will earn you some money , it's bad thing to start.
3. Hunting Giveaway, this make bitcoin looks bad , just do some effort .
4. Signature campaign, this is the best option so far
5. Mining altcoin would be additional option for everyone to earn bitcoin. do some research and do it!

goodluck