Brake line flaring isn't nearly as difficult as some people make it out to be. The savings from replacing just one bad metal line can more than pay for a quality flaring kit like the Matco DFS260 I use.
The Matco DFS260 Line flaring kit. Cost - about $70. Do NOT settle for a cheap $25-30 kit from Sears of your local parts store as the flaring bar and yoke are often cheaply made and won't work well at all. A good set will flare have adapters for 4-5 sizes and will come complete with a tubing cutter.
Begin by cutting the tubing with a cutter. Start with light pressure on the cutting wheel and make one full revolution with the wheel being the leading edge. In this case, I'm turning the cutter away from me. Tighten the wheel no more than 1/4 turn and make another revolution. Repeat until the tubing is cut completely.
Next, ream out the tubing with the reamer on the cutter or other suitable tool to remove any material left inside the line.
Finish prepping the end to be flared by removing any burrs with a fine flat file. Install the tube nut onto the tube and you're ready to make a double flare on the end of the your line.
Start by loosely clamping the line into the appropriate hole in the flaring bar. For this example I'm using 3/16" line, the most common size. The tube should protrude throught the bar and be level with the first step of the flare adapter. Once in position, tighten the wing nuts on the bar and snug them with pliers.
Install adapter into the line and the yoke on top of the adapter. Tighten until the adapter is flush with the cutting bar and then remove the yoke and adapter.
Reinstall the yoke on the bar minus any adapters and tighten by hand until it bottoms out in the line. Remove the line from the bar and you're done.
The finished product should be smooth and even all the way around and almost a perfect circle with the hole in the tubing centered. See, nothing to it!