bending 1/4" natural gas tubing
A tubing bender works quite well on this stuff and isn't expensive. An alternative you may want to consider for more open bends is an external bending spring if you can get one in the right size. 

Bending by hand is quite likely to kink the tube and isn't a good idea. 

What is the tube made of? It doesn't look like copper in the picture. Aluminium won't bend nicely or at all, steel needs a tool even more than copper. 

When using a pipe bender on thin stuff, take it easy and release the tool a few times rather than trying to make the whole bend in one movement.