One of the most aggravating things to deal with when writing a song is coming up with proper transitions, usually between verses and choruses. However, transitions can also occur as key changes, progressions, and tempo changes. This is not an exhaustive tutorial on the subject matter but rather an overview of some of your options.
Regardless of what kind of change you are dealing with, you should always consider an intermediary change, or bridge. Yes, this adds yet another change and must now also be connected with, both, the preceding AND succeeding parts. However, the intermediary part is usually a lot less musically dense, so it should be easier to lead in and lead out of than simply conjoining two completely disparate parts. Sometimes this bridge is as simple as a stripped down drum break, or even easier, a 1 or 2 bar sweeping effect. That is usually the best option if the chorus (for example) contains elements familiar to the preceding verse. If your chorus sounds a lot like the verse, there is no sense in drawing-out the suspense and tricking the listeners ear into anticipating some sort of big event (which will likely be a letdown if it sounds much like what was preceding it).