If the trailer is wagging, then just ease off of the throttle. A speed (55-62 mph) that one can "ease off from" is the key.
Improper load balance is the reason.
http://www.sherline.com/lmwkshet.htm
http://www.sherline.com/lmbook.htm#refrn23
http://www.klenger.net/arctic-fox/weight/index.html
http://www.nhtsa.dot.gov/cars/problems/Equipment/towing/index.htm
http://www.motorcycletrailer.com/mag1/DMVlinks1.html
What you "recall" is the admonition, with electrically-activated trailer brakes, to go WOT with the trailer brake control jammed over to fully on, fully engaged to cause the trailer to track straight. It is a last minute, desperation tactic, tends to ruin the trailer tires, and damages the trailer brakes.
I forgot to add above that the tires (all of them, tow vehicle and trailer) need to be less than 6-years old, have no evidence of sidewall or tread damage, and balance out properly.
The brakes of both should be examined, cleaned and relubricated prior to adjustment.
The electrical system should be checked with a SNAP-ON scan tool, and (my preference) all exterior lamps replaced.
Xtra-brite trailer lights are a
real, real good idea. The headlights need to be re-aligned for nose-high attitude (unless one is using a weight-equalizing hitch).
The cooling system should be flushed out, and the ATF and PSF changed/serviced.
Oil & filter are a good idea, but lubing the chassis, checking alignment for positive wheel return, and having an excellent spare tire and some flares or warning triangles is better.