It doesn't matter how interesting your characters are, if they don't make a splash when they first appear.
When you introduce a character, they need to leave a strong first impression. In their first scene, you need to tell your audience who this person is and what they're all about.
This doesn't mean it can't be subtle or clever. It just means that whatever your character does, that should encapsulate them. Let's give examples by looking at some of the cast of Winnie the Pooh.
If you were introducing TIGGER for the first time, what would you do? Tigger is a loud, boisterous, fun-loving tiger who loves to BOUNCE, so...
When he appears, he should probably be loud, boisterous, and indulge in one his infamous bouncing tackles. He shouldn't just walk in and say hello.
What about Eeyore: a slow-talking, tired, and incredibly gloomy stuffed donkey?
Well, he should probably demonstrate how gloomy he is. He will throw out some deprecating remarks, slouch, and generally seem like a sad sack of potatoes.
And what about Winnie the Pooh himself?
He is innocent, jolly, endearingly dimwitted, likes to sing, and loves "HUNNY". So SHOW your audience that, the second you meet him!
It takes a lot practice to get this right, but it's important to try early on. To show your audience as much as you can as quickly as possible, remember also the word:idea ratio (see that chapter for more), because you've got to keep things moving. Don't tarry!
Another tip to make your intros memorable is to SPREAD THEM OUT. In the very first Winnie the Pooh film, we are introduced to each of the characters individually. So, allow each of your characters to hold the spotlight before bringing in someone new. It really helps, no matter the genre or the story!
A word of caution, though. Don't forget who the main character is. It's great to have a rich cast of players, but don't let them get out of hand!
It's probably worth talking about this, actually.