I really like the triclopyr/clopyralid foliar mix. If you have trees that are single stemmed and still smooth barked at the base, the stem spray method may be more effective. For multi-stemmed trees, and trees already showing rough bark at the base, the foliar spray is the way to go.
For foliar spray, I usually mix mine at 1/2% each, with 5% diesel, and enough dish soap to adequately emulsify the diesel. The dish soap also acts as a surfactant, and the diesel a penetrant. I've tried a couple different brands of dish soap, and Dawn has been what I've had the best luck with.
I try to spray when the soil temperature 10-12" deep reaches 75 degrees F or higher. In my neck of the woods in North Texas, that's usually right about the July 4th weekend.
I avoid spraying when there is a lot of active growth in the canopy. This includes after a rain when there is a lot of light green growth on the canopy, the trees are in the white flower stage, and the trees are putting on beans. If the canopy is mostly a nice, dark green color, the trees are in the yellow flower stage, or the beans have fully elongated, the trees are more susceptible to spray.
I prefer to spray in the morning or late evening. If there is dew on the leaves, I wait for it to burn off before I start. I do this for two reasons. One is it is cooler on me spraying if I'm doing something else in the heat of the day. The other is hot temperatures increase the amount of volatilization of your spray. I want your spray to penetrate into the plant, not evaporate into the atmosphere.
I use blue dye. It makes it easier to see what leaves I've hit and what I've missed, and it also temporarily marks the trees I've sprayed so I don't accidentally double cover some. I make sure I hit every leaf.
As birdman said, I go back through the area twice. Once one week later, another two weeks later. If I missed anything, I hit it again during a walk through.
I really like to spray by the sign if possible. Sometimes, things just don't work out that way for me. Either I've got too much, or the sign just doesn't fall at a time I can get it done, but I think it makes a lot of difference.
Understand that spraying is not grubbing. I don't get a 100% kill every time. But most of the time, I'll successfully kill 90-95% of the trees I spray on the first pass. Some of them will try to leave out again and die. It takes 2-3 years to accurately measure what I've killed and what I haven't.
If the plants have been previously top-killed, they are hard to kill with spray. I usually give them 2-3 years to recover before hitting them with spray. It takes a while for the canopy to catch back up to the root systems, and get enough growth on the canopy to get adequate amounts of chemicals in the plant to kill the roots.