The most safe way to earn bitcoins, IMO, is to create value, and sell that for BTC.
This depends on your talents, but you could create real-life objects, products like arts/crafts or a useful website etc. and get BTC for them.

The second safest maybe with some kind of advertising like signature posting or other social media exposure. You can then put an affiliate link to something people would like to use. And then just be active in the community.

Investing is risky, do it if you know what you're doing, or if you did a LOT of research.

I would recommend to stay away from any gambling/casinos as you will most likely lose in the end.

Take care.