Many ways to earn bitcoin, mostly people earn by signature campaign because that doesn't need any skills. But signature campaign won't give you big amount of btc.You should do trading to earn big because only trading can give you good profit in quick time.
Not only trading that can make you earn good profit, investing in an ICO is also good way to grow your bitcoin. Both are risky, it depends on how we choose where to invest or what/when to trade.
yes that is right that both are trading and both are equal risky but i will add that gambling can also give a good profit to you if you have some good experience and skill in gambling, only depending on luck is also not a good decision, as in gambling there are so many games where your skill and experience is necessary.