Hi Pd. Cut below the leaves and above the next junction/leaf set. Strip off the leaves on your cutting flower and voila: longer stems. You can also pinch out the top set of new little laterals going down a particular branch (below the bud/s) and get a much longer stem that way. Or two sets for really long stems.
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cut above next leaf set for new laterals
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Even if you don't see laterals deep down into the plant, I bet they are there, waiting to emerge. On shorter plants, that might not be the case, I don't know.

thanks so much for the pictures. It is so much easier to tell me what I need to know. The top picture has me baffled on some of my dahlias. I want more flowers and I only have that top to work with which shows no laterals if I pinch that little area. I usually just let it go. I have some with very long stems, down into the main part of the plant. Leaves a big hole where I cut. I than take a little piece of a leaf branch and fill the hole. We have had tons of rain. Hopefully won't get root rot. The dahlias are great this year. I have found that some don't match the label which really annoys me. Anywhere there is a pink and yellow dahlia, it is an incorrect tuber.