1. Buy cryptocurrency (the good one), hold for a while, and sell when the price go up. Buy low, sell high.
2. Mining. You can build a mining rig and earn cryptocurrencies automatically. However, the cost of building a proper mining rig is expensive nowadays.
3. Work. offer your service/product on this forum (marketplace section).
4. Freebies. You can earn cryptocurrency from a faucet website. You can also join a campaign to earn new kind of cryptocurrencies.