What kind of mouse do you have? I once had a mouse that was "slant" so that the buttons were on different heights. It was nearly impossible to press both buttons exactly at the same time which is required for DSJ. Now I only play with perfectly symmetrical mouses.
Other than that, I guess its just about timing. But you shouldn't take too much advice from me, takeoffs are still my biggest problem too

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EDIT: Oh yeah and I also rememberd another thing: anti-aliasing causes some minor lag for me (not very powerful graphics on my PC) and if I have it enabled, all of my takeoffs are a bit "later than expected" because the visual response is too slow.