Look at the wire itself. One conductor will be differentiated fromt he other. It could be one has a stripe or ridge down the length of the wire, one wire may be colored differently than the other, or there may be a thread in ones conductor that isnt there in the other.
This is so you can keep track of the wires. Most people use the stripe (most common) as positive but its really doesnt matter as long as you are 100% consistent.
So find what makes your two wires different and pick which one will be positive and then coonnect it to the + in the speaker and + in the amp end.