Finally, get a good teacher.
I am obviously biased here, but there really is no substitute for a good teacher. Not all fiddle players -- even the very good ones -- are good teachers. So find someone who has experience, and who understands not only how to play well, but how to teach.
While you definitely can learn to play the fiddle by yourself, there are many good reasons to take some lessons with a good teacher.
Firstly, if you are a beginner you will improve so much more quickly with a teacher, and this in turn means that you are much less likely to get frustrated by your progress, and perhaps even stop entirely. Playing is meant to be fun!
Secondly, learning good technique will mean to you can progress further. Bad habits can really hold you back later on.
Thirdly, if you have been playing for a while, or you played before but stopped, you may find that your progress has plateaued - you just aren't progressing as you would like. A good teacher can help you get to the next level.
Finally, a good teacher will motivate you, and make learning fun, not a battle!