typically, the positive wire is red and the ground, or negative, is black. However, most speaker wires don't do colors. Good news is, with speakers it doesn't really matter which one you choose as your positive and which as your negative, just so long as you are consistent. Ultimately, what you want is for the wire that connects to the red terminal on your Amp or Receiver to connect to the red terminal on your speaker.
I usually look for the wire in the pair that has the writing or other markings (sometimes a line, for example) printed on it. I pick that one as my negative wire and put black caps on both ends of it, putting my red caps on the other wire. Then, when I plug in, I am sure that the two red terminals are connected and same for the black.
Worst case scenario, even if that fails and you somehow crossed them, you likely won't even hear the difference. It has to do with what's called the "phase" of the speakers, it doesn't hurt them, but can sometimes mess with the sensation of stereo sound and make it hard to find a "Sweet spot" to listen from. That's all.