Just found this good description at http://weldingweb.com/showthread.php?260681-Oxy-propane-neutral-flame&s=befe41b455db6bd0a0d81000b461b614&p=2599701#post2599701 -- putting it here to share and bookmark.
Setting a flame with propane is not as difficult as most people make it. It is different than acetylene though. You open your fuel and light it, adjusting until you get a stable flame pushing out of the torch. Then you slowly open your oxygen. The flame can be judged based on the shape and color of the inner primary flame (or flames for a rosebud). When the primary flame is long and has a feathered border, it's reducing. As the primary flame becomes short and well-defined, it is neutral. The oxidizing flame looks really similar to a neutral flame, except the difference is that the oxidizing flame will have a slightly shorter primary flame and the primary flame will become a brighter/lighter (whiter) color blue.
Practice going through the full range of reducing, neutral, and oxidizing while slowly turning the oxygen knob a few times. You'll get the hang of it.
Once you know how to judge the oxy/fuel ratio - it's just a matter of getting used to setting the fuel flow high or low enough with the torch knob so that the flame is stable (not pushed too far from the torch, and on a rosebud, there will be a ring formed by the back ends of all the primary flames) but is pushed out from the torch tip enough so the combustion is happening outside the tip.
Setting a propane flame should not take any more time than an acetylene flame.
I don't use oxy/fuel cutting equipment. I mainly stick to oxy/propane brazing with single flame and multi flame nozzles. Always read your entire equipment manual in case there's something special about adjusting your cutting torch. If you don't have a copy, you can find most online.
Also, remember that in acetylene, the primary flame has lots of BTUs of heat, so people are used to applying the primary flame to the work. In propane, the secondary flame has all the BTUs of heat, so you want to apply the secondary flame to your work surface to really apply some heat. Lots of people make the mistake of treating a propane flame like the primary flame of acetylene, they put the propane flame too close to the work, and they come away with a bad experience where they think propane is lacking in heating power. Propane has a large and high BTU secondary flame which is great for applying lots of even heat to chunky assemblies - which is great for brazing or preheating for cutting on thicker metal.