I follow one simple rule about my shows: The PCs are the stars of the show, so they need to be in the middle of the action as much as possible.
For landing parties, that means that the PCs are usually the ones who find themselves heading planetside just about every time. Kirk and Spock often beamed down together, and also quite often with Bones in tow. I try to do the same thing.
In the 2280s game I'm running, I have four PCs (the last two episodes featured the captain, first officer (who's also security/weapons officer), helmsman, and chief engineer...this episode has one player leaving and another joining, but we'll go with the listed group above). So, I design my episodes with the intention that landing parties will benefit from having the former-scientist, the security guy, the engineer and the pilot around.
Now, the first officer's player didn't mind staying on the bridge when others head down, but I've worked the episodes so that even he was involved as much as possible when left behind.
I'm losing my first officer player, so he'll end up being the "eye in the sky," and the landing party will now have our erstwhile Tellerite surgeon (yes, his bedside manner is terrible...) along for the ride.
The point is, all of the PCs should have as much screen time as feasible. So, even if the situation planetside has no call for one of the PCs to be present in the landing party, be sure to give them a problem to solve on the ship.
You take a look at my game here.
Davy Jones
"Frightened? My dear, you are looking at a man who has laughed in the face of death, sneered at doom, and chuckled at catastrophe! I was petrified."
-- The Wizard of Oz