How can I make sure that the scores I compose...

Each movie? Hell, each scene! Rely on the movie itself for inspiration.

Why? How many movies have you been hired to score?

Glasgow's FOREMOST authority Italics = irony. Infer the opposite please.

Well, I want to compose the scores for the movies I direct, so technically I haven't been hired.

Well then if that is all you want all you need to do is get one of these (or one similar to it) and have at it. You can do a full film score on one of these with any instruments and sound effects you want.

https://www.youtube.com/watch?v=XeMcbhXvLsM

Or if that is too much trouble then get in contact with Clint Eastwood, he composes music for films he directs. Maybe he will share his technique with you.

..*.. TxMike ..*..
Sometimes I think we're alone in the universe, and sometimes not.

So if the only person you need to satisfy regarding the music is yourself, why do you need us to tell you how to compose?

Glasgow's FOREMOST authority Italics = irony. Infer the opposite please.

1) It's not about satisfying. I can't be as objective about the quality of the music as if I was hired by another director.
2) There's a line between an artist having trademarks and an artist repeating themselves due to a lack of talent. I don't need you to tell me how to work; I just want tips from people with more experience to make sure I don't cross that line.

What has objectivity got to do with satisfying yourself? Are you asking how to pretend you are composing for a director who wants you to follow the rules, rather than for yourself, who doesn't know or understand the rules?

Essentially you're asking us to tell you how to tell yourself what to do, if we were you, even though ultimately you only have yourself to satisfy because you're the director.

"I don't need to believe it's real. I just need to believe it."

This isn't about satisfying myself. If a composer's works all sound exactly the same then he's not a very good composer.