Anything that you can do to earn fiat currency can also apply to Bitcoin or altcoins because they are also a currency. If trading and mining cryptocurrency is not for you, there are websites that you can work as freelancer online for cryptocurrency related companies that offers Bitcoin as your salary. Another way is if you have an online store or you can offer something useful or services, you can accept Bitcoins as alternative way of payment. If you have money to buy Bitcoin you can use it to do lending and make profit from interests.