Once you've done this a couple of times it's easy. If you need to cut the spring first a dremel rotary tool or similar with a small cutting disc should do the job; it's what I use. I tried a hacksaw once but found it really difficult to get it to bite into the steel. Maybe slipping the spring over a length of wooden dowel before putting it in the (padded) vice jaws might help if all you have is a hacksaw. Before closing up the last coil with heat I like to tidy up the cut end with fine files and maybe wet and dry paper so that there are no tiny burrs where the cut end meets the next coil. Then of course do a final finish after the spring has cooled down. If the spring will stand up by itself on the newly-finished end you will be doing well; if it is vertical then so much the better.