I second several of the above suggesetions. Get the tool (check out a recent thread on this subject, and get a GOOD tool), read the instructions, and get some scrap pieces of brake line to practice on. Take extra care filing the chamfers on the ends of the tube.
Don't shave pennies trying to reflare old rusty tubing that can easily be replaced. If you must do it, cut it off short where it's clean and accessible, and add a piece, rather than trying to stretch the old piece to fit.
And finally, get a GOOD set of flare nut wrenches. None of that Walmart or chain store crap, even if it's warrantied, and maybe not even Craftsman these days. The fit must be perfectly tight, and the wrench can have no spring in it. Get Snap On or SK - even at 12 bucks or so a wrench it's worth it. Then take lots of time on fittings. Even if the fitting comes loose, if it doesn't rotate on the tube, it will ruin it. It can take a lot of wiggling and back-and-forthing sometimes to get an old rusty fitting off alive.