This tutorial will apply to all video-editing softwares. Also, this goes along with timing, if you haven't read that yet, I suggest you do. Although you'll probably understand even without reading it. Moving on, what I'm going to talk about is what type of transitions to use and such.

First things first, you do not want to experiment with transitions. When it's a romcom, some will try using the box transition, hearts, or something like that. Don't do that. Since Sony Vegas doesn't have the best transitions, (unless you get blue fx, which also costs money,) I usually only use the crossfading effect or no transitioning at all. (Depending on the song.)

In between songs where they are singing or it's the chorus, that's where I usually don't crossfade. l don't really know how to explain it, but when there are scenes that transition abrupty, that's where you should use crossfade.

Sorry for the failed & short explanation >.< Feel free to ask questions.