I was brought up on a healthy diet of science fiction. Both my father and grandfather loved the genre, and any tv series, film, or book, was readily devoured.
One of the stand out features of the original Star Trek series was the anticipation of seeing the bridge for the first time in each episode. If Mr. Sulu and Mr. Chekov were in the driving seats then nothing much was going to happen. However, if there was an unknown crew member sat next to one or the other, then you knew something dramatic was going to happen and they would soon be dispatched.
If the crew members had a name you knew they were safe. If they didn’t they died. Simple. Throughout the series all of the supporting characters featured in episodes with stories based upon them.
How are your supporting characters doing?
Are the just a name? Is there purpose just to be dispatched, so your main characters can get on with the story?
If so, maybe you should reconsider them.
Any successful business or sports personality will be quick to praise those around them, their teams which support them. Even actors receiving accolades usually reel off an impressive list of people to thank who have supported them.
Your main characters will be stronger and more impressive if you put more care and attention into their supporting cast.
Given them a more solid back story. Give them more of a role than just to be the guy who accompanies the protagonist and then takes the bullet which saves them in the ambush, or the female character more to do than run around in the wake of the hero.
The more real you make your supporting cast, the stronger performance they are allowed to give, the stronger your story will be, and the better your protagonist will look.
I don’t mean giving them a fuller set of biography notes, but make them more realistic in their presence and contribution in your story. Let them do things which are important to your plot. Let them say things which contribute.
(There is always a place for the unknown guy/girl who is going to make it past page twelve though!)