To earn money with bitcoin you can do some works if a person needs help with something or just look for a job you might have luck finding one here in this forum.
Just buy Bitcoins at a low price and save them for a while. When the price goes up you can sell them at a profit. It can take a while before this happens but you just have to wait it out.
Trading is good way but you need initial capital and decent knowledge of the subject to earn money.,
well i think it depends on what you are doing in order to earn your bitcoins, i think that you dont need your knowledge about it all the time because it might not be connected with bitcoins
i also think that the best way to earn your bitcoins is by doing some small work for bitcoins that you would be paid in fiat or you just could participate in some signature campaigns