Before bending copper tube it should be annealed using a heat source such as a blowtorch or Bunsen burner. The blue flame should be played evenly and slowly over the length of the tube, stopping just before the tube becomes red hot.
Before bending the pipe it should be filled with fine grain dry sand to prevent compression of the tube. With very small bore tube, the tube should be wrapped in wire before bending instead of using sand. In most cases the tube can be bent by hand with satisfactory results, but if you need a neater appearance you should use a jig. For example, it is common to put a spiral into fuel pipes to hold more fuel in the same space after the check valve. To make the spiral obtain a 1" dowel and wrap the tube around the dowel several times in layers.
You can also bend tube using the spring devices you get from hardware stores. Some are designed to be inserted inside the tube and others have the tube inserted in them. They stop the walls collapsing at the bend by filling it or holding it from the outside. I've tried both and putting the device inside seems to work best. Make sure you choose a spring that is a loose fit so you can get it out after the tube is bent.
Some types of union joints require the tube to be flared. This is very easy with copper tube. You can either use a flaring tool which you may find someplace which sells old tools, or you can do what I did and drill a hole into a piece of 5mm steel plate the same diameter of the tube. When complete take a drill two sizes over the diameter of the tube and drill a 2mm deep countersink over the other hole. Slide the tube to be reamed into the hole with the end of the tube slightly above the surface of the plate. Secure the tube in a bench vise with the plate sitting on top of the vise. Insert a centre punch into the tub and whack it - done!