Here's what we did on Intrepid, take it or leave it as you will.
None of us had any professional training or experience (obviously) so we pretty much made things up as we went along, learning what worked and what didn't (for us). Since I was writing the script, I made a conscious decision to tailor everyone's characters to best suit their abilities. Most of the cast didn't have any acting experience (those who did only had stage experience and weren't professionally trained), so I tried to give them stuff to do that would play on existing relationships between the actors, in the hope that it would be easier for them to put themselves in the moment, and hopefully turn in a more natural performance. I think, for the most part, it worked.
As far as the script, I mostly bounced ideas off Steve who was directing (and is a pretty talented writer whose judgement I trusted, and who wouldn't be afraid to tell me I was wrong). Everyone would chip in with ideas at read throughs, and if they had useful suggestions I'd take them onboard. If they weren't useful, I had no issue with saying no (and often did). Nobody objected if I said no, though they didn't always agree. Regardless, there was an understanding that the final decisions sat with Steve and I, and once we'd made a decision it was time to move on. When it came to shoots, the same applied, and we usually tried to give folks a chance to chip in (within reason). That said, I suspect there are times we probably missed good suggestions due to time constraints.
Steve spent a lot of time looking at movies and seeing how shots were framed, and how scenes in various movies and TV shows were cut so he could apply that to how he framed his own shots, and how he cut the final video together.
Ultimately, I don't think we did too horribly for a bunch of amateurs with no experience, training or professional kit. But I'd be an idiot to think anything we've produced could compete with even the lowest of budget professional productions. That said, we very quickly learned what works and what doesn't, even if we couldn't always put it into practice.
And while I would agree that a professionally trained actor or writer has a huge advantage, that does not mean those who lack that advantage are universally unprofessional or lacklustre in their work.