While I think slide film is better for learning in that you see the direct results of your exposure decisions, I would agree with the suggestion for negative film. It's a whole lot cheaper to buy and to process, which means you can shoot more frequently, which in turn means you have more opportunity to get better at it. Unless cost is not an issue.
The only thing I would disagree with in terms of what AC12 said, and it's a nit, is the suggestion to use short rolls. My experience is that there is so little difference in cost (both film and processing) that you might as well use 36 exp rolls (you can validate this with your own source for film and processing). BUT don't wait to have it processed; if you have to occasionally waste 8-12 frames, it's a small price to pay. If you were bulk loading film and processing it yourself, I'd agree with the short roll suggestion.
If you're doing a lot of low light photography, you might want to consider ISO 400 film.
Since I assume you don't plan to process your own film, at least for now, you have to consider where you get the film processed. I don't know where you're located, but serious labs are getting few and far between. Mail order processing takes too long to evaluate and learn. So that leaves a minilab. Find one that is close and does reasonable volume. I like Costco (they treat their employees better so they stick around longer) but it's really dependent on how much volume they do and how much the "tech" running the minilab cares. If you find someone good, bring it to the minilab when he/she is there. If you have an independent camera shop with minilab, all the better.