I bought a bunch of logic level converters for 3.3v to 5v as part of a first robotics team project:

So with a serial connection you have to connect the Tx from the sending device to the Rx of the receiving device.  This level converter is labled with a bunch of Rx and Tx, however there is only one correct way to wire this device.   I got very confused...   So for me next time I use one of these or possibly for you if you are also trying to figure out how to connect this up, I present you with the following:

You have to do the Rx-Tx switch on the low voltage side.  Basicially hooking this module up any other way will not work.

The neutrals are drawn as separate, but they should actually be common. They are also drawn with a ground symbol, cause that's how the board is labeled; but they are not ground wires, they are actually neutrals, but nobody cares. :-)

Good luck!

These are so cheap, here is a pack of 10 for $5.