I need help with movie transitions?

Well, I'm making a for fun movie so it's not actually a going into theaters movie. I just need help on how to make the transitions natural, and in place ya know what I mean? It's kinda like.. I don't wanna overdo transitions and scene switching. Hard to explain but yeah. Also, I absolutely need help on music transitions.. sometimes theres music in the background and sometimes there isn't. I never know at what moment to change songs.. and what moments to not put music it. It's a problem for me.. if you could help me that would be appreciate. :)