Dealing with "Stun Lock"
In game systems that use initiative, nothing is worse than having your character taken out of the action. It's bad enough that your character is either dead, dying, paralyzed, or unconscious. But on top of that, there's 20 minutes of combat left, and you don't get to do anything.
I loved 4e, but one of my biggest gripes about it is that as you gained levels, stun-lock became an increasingly powerful player tactic and an increasingly common monster power. When the monster loses their turn, no big deal -- the DM has other monsters. When the player loses their turn, they've just had 5-10 minutes go by without any input into the shared fiction. And that sucks.
So what can you do?
The pain of "not getting a turn" is the pain of not getting to contribute to the shared fiction. The solution is to give the player input into the fiction in ways that have meaning and impact.
If there are any NPC combatants on the PCs' side in the fight, let the player whose character is out of the action play an allied NPC.
It's less obvious what you should do if there are no NPCs in the fight they can take over.
If the player's character is out of the whole fight, such as if they're in another scene that's not in initiative rounds, or if they've been killed, let them play one or more monsters. Players will love this. If you only have one monster left, work with them as a team. "Who should we attack? Really? Isn't it better to take out that Rogue who keeps stabbing us first?"
If the player's character lost just one turn, or if they'll probably lose only one or two turns, ask for their input on things: "Should the lich use Cone of Cold or Confusion? Which do you think would be best?" They're paralyzed. It's not going to affect them in the short term. They should be able to keep a clear head about it.