The only safe way I know and the most people also using is doing signature campaigns, they are easy and risks free.
If you do other methods you mostly also need to risks things and invest some money.
Not only signature campaign is safe and low risk you can also doing some bounties in our altcoin section that can help you to earn more bitcoins just to collect altcoin and exchange them into bitcoin.
That is a best and easiest way of earning some bitcoins but they are really much lesser bitcoin we have to go to trade for increasing our bitcoins or have to learn some other skills to increase our bitcoins and to be able to live with these bitcoins.