The wheel is like a suspension bridge, it really wants the spokes as evenly tensioned as possible. Is the wheel rim bent from use or is it just not properly trued from new? How out of true is it? You can true a bent rim by using the spoke tension to pull it almost straight, but it will be weakened by the uneven tension. The actual amount of truing you can do this way is a matter of opinion, because its a trade off. At some point though its better to just buy a new rim because you want even tension. You can loosen off all the spokes and try straightening your rim a little by hand, bending it over something solid, a log or whatever. Then tighten it up again and hopefully the spoke tensions won't need to be too uneven to pull the rim into shape.