As Ralphy says, good tools are a must. I picked up a Lisle brand flare tool at the parts store for about $40.00. Worked fine. Make sure the tubing end is square and burr free after you cut it. I used a file to clean up the end after cutting and also to put a slight taper on the tubing end before flaring. Also a drop of brake fluid on the die helps.

You will make a few mistakes, just take it in stride.

The 51's went to 3/16" lines. My 50 was all 1/4" and my 51 3/16".