Funny enough that Eryth answered that question just one page back.
I take it after watching that video phiny posted and that you have practiced for awhile you know how to perform it. Here was a method I found that reduced the number of inputs and might make it a bit easier.
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Control stick position, with 5 as center.
While standing, dash by pushing the control stick into the 1 or 3 postion and hold it there.
After the dash happens, you want to c-stick down for the dash attack, then press your attack button.
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Control stick in 1 or 3 position registers as a dash. But, after the dash happens, holding it in that position gets treated as holding up. So, the only difficulty with this method is making sure you hit the buttons in the right order and with the right timing. I usually found that rotating the control stick up added more area of error. This method gets rid of that extra need of moving the control stick up after dashing.
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