For what purpose? How you do it will depend on what you'll do with it, though your options will be somewhat limited considering the very low voltage. The easiest way would be a voltage divider (two equal resistors in series with the voltage, tap the 1/2 Voltage between them) but that will only go so far...
both suggestions would do in reducing the voltage supply by about half. the diode would give a voltage drop of about 0.65v. for a voltage divider if you use a 1% tolerance you would probably get half of whatever voltage your battery have and you have to consider the heat to be dissipated by the resistors depending on you load.
As John said - WHY! - any possible solution will depend greatly on what you are wanting it for, and what the current demands are - I suspect you may well be asking the completely wrong question?.