wheels that wobble
 

what is the best way to true a wheel with only a spoke wrench?

adjust your brakes so that they are perfectly centered, flip the bike upside down and insert wheel. true, using brake barrel adjustor as truing stand thingy.

flip your bike over and use the brake caliper arms to check the true. As usual, Sheldon Brown has good advice on this under the "Check the Rims" section of his article: http://sheldonbrown.com/tooltips/truing.html