DISCLAIMER: I don't make EDM, I make rock. But this advice should be general enough to still apply:
Find an element in the first part that can be repeated in the second part to sustain the transition. Sometimes it's one aspect of the rhythm, sometimes it's a little hook in the melody, sometimes it's a single note bridging a surprising key change.
Another approach which works well if the two parts are fairly similar, is to break for 1-2 measures into something TOTALLY different right inbetween the parts. (I think that's the purpose served by a "breakdown" in a lot of popular music.) For this to work, the end of the first part has to kind of hint that something else is coming up. Going into the "breakdown" helps distract people from the fact that the second part, which the first part was leading up to, isn't actually all that different.
A third way to do it is gradually slow the tempo down toward the end of the first part, during the last 1-2 measures. This throws the listener off and makes it so it's harder to predict what's coming next.