Buy BTC when price lower, and hold coin!
that is true and you make a lot of profit if you do that.
but the question is mostly about how you can make (earn) bitcoin. for example if you have a skill and use it to get paid with bitcoin. or my favorite if you are into trading altcoins how you can make lots of bitcoin profit by trading them.
Buying bitcoin is favorable only to those who have a capital to invest but most of us are relying on jobs only to earn something and sometimes we cannot even set aside for investment due to the fact that we have to priorities our needs. I believe to earn requires deep knowledge and hard work, we have to abuse every opportunity we can find here and save the rest after expenses to be consider as our income that will have a great value in the future.