Originally Posted by bkbrouwer
Take a trip to Home Depot. Get two little spring claps (I think a four pack is $1.99). Clamp some objects (screwdrivers, allen wrenchs, popcicle sticks, whatever) to your forks or seat stays (as applicable to front or back wheel). Set them so they touch the rim on both sides, spin the wheel slowly. Where the out of true section is one will get pushed out a bit, the other will have a gap. Adjust. Repeat until they stay in contact with the rim.
You can also align them with the top of the rim to see where any flat spots might be.
Take a marker pen, hold it against the brake just shy of the wheel, spin the wheel, then slowly bring in the marker pen. Stop when you first start touching the tip of the pen with the rim. You'll have a great visual indication of where to true. Fix, repeat, fix, repeat... Will do a 90% job without a truing stand.