I would recommend taking a short workshop (1 or 2 weeks) at a local tech school or community college. You get the basics, safety info, experience with some good stable equipment and a little supervised practice time. Then go get a decent welder (and they are pretty inexpensive these days) and practice like brother Holohan stated - tons of different stuff and practice, practice, practice.... You will be amazed at how fun it will be.
And build yourself a decent weld table to start with:
https://lateral-g.net/forums/showthread.php4?t=24523
Jim
PS, I forgot - read everything you can get your hands on. But that rule applies for everything fabrication - so you should already be reading every day, there's no end to learning.