A common mistake that we see a lot in videos are jump cuts. By that I mean, it cuts from one shot to the exact same camera angle, the exact same shot, just a little bit later in the timeline and it's a noticeable jump. The experts head or body position is completely different and it's just very jarring to the viewer and just not very professional. When you are doing cut away shots, when you are editing your video, avoid jump cuts at all cost. Cut into the close up or to a different angle, wider, closer. Try to avoid cutting from one wide shot to another wide shot. It's very choppy.
The same rule for jump cuts applies to the use of dissolves. Basically, you don't want to cut into the exact same shot and you don't want to dissolve into the exact same shots. So use dissolves sparingly, only when needed, when it really helps smooth things out and don't go over board with that. Always remember, it's best to cut in or dissolve to contrasting shots than the exact same shot or camera angle. I will go through the timeline. At the very end, you will notice right here is a fade-out. Now how you would apply that, is you would go over here to your Effects tab. You would go down to a Dissolve tab; you would open that up, and then Fade In Fade Out Dissolve. There it is. You can just drag it over to the beginning or end of your clip and let go. There it is.
Now by default usually, in Final Cut Pro at least, it's 1 full second and that's a fade out.