The most effective way is alway to earn $$ in real world and then buy eth with it, or if you have any crypto skills, you can earn some crypto from it.
If you want to have eth without using any cash, it may be slow but it is still doable
- joining faucet or airdrop, you will be able to gain like $0.10 per action so if you spends hours in it, you can gain like $5 of eth.
- participate in bounty campaign to earn tokens to convert to eth. This will be more feasible cause you can gain like a few hundred of $$ for some twitter campaign and even thousand for signature campaign. However, you will need the necessary resources like twitter account with thousands of followers.
- sell your items online for eth. who knows, maybe you have some valuable possession that can exchange for significant eth.
- invest in ico and hope to profit in eth, so when you convert back, you will have more eth. however, this will not be easy to spot profitable ico.
- invest in passive income like neo or alts that gives dividends. convert these dividends to eth.