Hi,
fungus' original recomendation was you learn some general coding. You should be advised that the question you've asked is a really tough one to answer, likely to recieve alot of varied feedback. I agree with Retrolefty's suggestion with some caveats. C is probably better to learn first if you will just be programming the arduino. If you wanted to write programs for other things, like computers or phones etc. it's arguably not the best option.
Learning C first is fine as long as you understand that switching to C++ down the road will require that you change the way "you think about designing making your programs work." Which can be really tough for some people as it imposes a bunch of new rules that are hard to make sense of at first... These new rules tend to make it a more powerful language because you can manage Complex programs easier and thus is more productive. So if you do end up learning C first, always keep that in mind and don't forget it. You may want to do a bit of research on the differences between the languages and their "programming paradyms", then make a decision. One final thought to consider- today, many microcontrollers like the arduino are still generally limited by its resources which is why C is so widely used. In the coming years as the MCUs continue to evolve you may see a greater shift to Object Oriented design. Again, these are just my personal opinions and recommendations.