Simple question anyone?

Just left click somewhere other than a note.

You're talking about going to PRV by double clicking a track, and the whole thing is selected/highlighted.  As FBB explained, you click anywhere other than a note to de-select everything.  You can tell when notes are selected - they turn black.  But you'll find yourself getting a whole clip or track re-selected when you don't want that.

That's why for me the easiest way to work in the PRV, and that's where I do most of my work, - is with one track of the Track View visible above it.  I scroll to the track I'm working on so I can see the TV version of it and the PRV version at the same time.  I can easily click the header of the track in TV do select or de-select the track when needed.  Having that semi-split view comes in handy for many reasons.

I work in the other direction though - I have PRV open, and open the tracks I want to work on through its menu.  Notes/tracks don't come up pre-selected that way.  Once you're there in the PRV, it only makes sense to continue your MIDI editing by using its menu to select other tracks, add tracks etc.  And when I switch tracks I'm working on, I scroll in that one track of the TV visible above so I have the currently selected track visible in its horizontal TV version.  WizMouse makes the scrolling painless - free app that lets you scroll wherever you want without having to click to focus on a window.

I do go on.

RB

Thanks guys, very helpful!