Anything other than signature campaigns and gambling.
A bit saved is a bit earned. So save your money by not clicking on any of the signatures of the people posting in this thread.
For me, the greatest way to make bitcoin would always be mining, because the earnings in mining is enormous. Although, the only problem I see with it is the fact that it takes money to maintain a mining system, not to mention the expenses paid for the electricity bill every month. Still, it is really and definitely worth it.
It is good to have this spirit to use bitcoin no matter how you use and which feature you use for bitcoin. if you are good at mining and you have an experience in it then it is good for you but if you are not good at mining then it has some side effects as well, mining cost a lot of money to maintain the system as it needs proper equipments for mining and it use a lot of electricity in a lot of watts so I think it is not really advisable to use mining , I would prefer to use bitcoin investment instead of mining as the profit is same but it does not cost anything but your capital to invest and the patience to hold.