Well some general guidelines....

Have a release on both sides.

Place the tow point on the tow plane near the CG. If you're towing with a Cub for example, you'd place it at the tailing edge of the main wing on top of the fuselage. Keep the line clear of the elevator, you dont want it getting under the stab.

There's guides at RCAT that will explain in a lot more detail.

You might enjoy this if you're getting into aerotowing...

[youtube]http://www.youtube.com/watch?v=dUIGEay0D0w[/youtube]