Four points:

(1) Detect Evil is not constant. It requires concentration.

(2) In general I believe that players have more fun if I let them use their abilities explicitly. Getting a good result on a die roll is fun, and making the roll that lets you notice something lets you feel like you've done something useful for the party.

(3) Unless there's a really good reason to keep something secret, I assume that what one party member knows they all know. Knowing things is more fun than not knowing things, and in particular it's not a good feeling when people are passing notes around to make sure you don't find something out. It's also much faster to just say things than to pass notes around.

(4) For encounters with NPCs, I try to make sure there's always something at stake: something the party wants from the NPC, or something the NPC wants from the party. Otherwise the group kind of stands around staring at each other, wondering why I've just narrated this scene where they're supposed to be talking but there's nothing to talk about.

Here's what I usually do:

Me: "You enter the room and there's an old man in the corner, talking to 
   himself.  He looks up and smiles at you.  He says: 'Guys, I need your help.  
   There's a monster in the next room and I need you to kill it...'"
Fighter: "Does this guy seem trustworthy?"
Me: "Roll Sense Motive."
Fighter: "Um, 7."
Me: "He's not obviously lying as far as you can tell."
Paladin: "I use detect evil!"
Me: "You're catching some very faint evil.  It doesn't seem like this guy is
   personally evil -- he's certainly not been using any evil magic -- but he 
   might have been exposed to something evil recently?"
Bard: "I roll Sense Motive.  I got a 28.  Does this guy still seem trustworthy?"
Me: "No, he's totally lying.  There's someone in the next room and he's hoping
   to convince you it's a monster so you attack without talking to it first."

Four points:

(1) Detect Evil is not constant. It requires concentration.

(2) In general I believe that players have more fun if I let them use their abilities explicitly. Getting a good result on a die roll is fun, and making the roll that lets you notice something lets you feel like you've done something useful for the party.

(3) Unless there's a really good reason to keep something secret, I assume that what one party member knows they all know. Knowing things is more fun than not knowing things, and in particular it's not a good feeling when people are passing notes around to make sure you don't find something out. It's also much faster to just say things than to pass notes around.

(4) For encounters with NPCs, I try to make sure there's always something at stake: something the party wants from the NPC, or something the NPC wants from the party. Otherwise the group kind of stands around staring at each other, wondering why I've just narrated this scene where they're supposed to be talking but there's nothing to talk about.

Here's what I usually do:

Me: "You enter the room and there's an old man in the corner, talking to 
   himself.  He looks up and smiles at you.  He says: 'Guys, I need your help.  
   There's a monster in the next room and I need you to kill it...'"
Fighter: "Does this guy seem trustworthy?"
Me: "Roll Sense Motive."
Fighter: "Um, 7."
Me: "He's not obviously lying as far as you can tell."
Paladin: "I use detect evil!"
Me: "You're catching some evil.  This guy isn't as evil as, like, an evil
   cleric or a cultist or anything like that.  But it feels like he might be
   kind of a jerk.  Maybe he spends a lot of time thinking about ways to hurt
   other people?"
Bard: "I roll Sense Motive.  I got a 28.  Does this guy still seem trustworthy?"
Me: "No, he's totally lying.  There's someone in the next room and he's hoping
   to convince you it's a monster so you attack without talking to it first."

Four points:

(1) Detect Evil is not constant. It requires concentration.

(2) In general I believe that players have more fun if I let them use their abilities explicitly. Getting a good result on a die roll is fun, and making the roll that lets you notice something lets you feel like you've done something useful for the party.

(3) Unless there's a really good reason to keep something secret, I assume that what one party member knows they all know. Knowing things is more fun than not knowing things, and in particular it's not a good feeling when people are passing notes around to make sure you don't find something out. It's also much faster to just say things than to pass notes around.

(4) For encounters with NPCs, I try to make sure there's always something at stake: something the party wants from the NPC, or something the NPC wants from the party. Otherwise the group kind of stands around staring at each other, wondering why I've just narrated this scene where they're supposed to be talking but there's nothing to talk about.

Here's what I usually do:

"You enter the room and there's an old man in the corner, talking to himself. He looks up and smiles at you. He says: 'Guys, I need your help. There's a monster in the next room and I need you to kill it...'"

Fighter: "Does this guy seem trustworthy?"
Me: "Roll Sense Motive."
Fighter: "Um, 7."
Me: "He's not obviously lying as far as you can tell."
Paladin: "I use detect evil!"
Me: "You're catching some very faint evil.  It doesn't seem like this guy is
   personally evil -- he's certainly not been using any evil magic -- but he 
   might have been exposed to something evil recently?"
Bard: "I roll Sense Motive.  I got a 28.  Does this guy still seem trustworthy?"
Me: "No, he's totally lying.  There's someone in the next room and he's hoping
   to convince you it's a monster so you attack without talking to it first."

Four points:

(1) Detect Evil is not constant. It requires concentration.

(2) In general I believe that players have more fun if I let them use their abilities explicitly. Getting a good result on a die roll is fun, and making the roll that lets you notice something lets you feel like you've done something useful for the party.

(3) Unless there's a really good reason to keep something secret, I assume that what one party member knows they all know. Knowing things is more fun than not knowing things, and in particular it's not a good feeling when people are passing notes around to make sure you don't find something out. It's also much faster to just say things than to pass notes around.

(4) For encounters with NPCs, I try to make sure there's always something at stake: something the party wants from the NPC, or something the NPC wants from the party. Otherwise the group kind of stands around staring at each other, wondering why I've just narrated this scene where they're supposed to be talking but there's nothing to talk about.

Here's what I usually do:

Me: "You enter the room and there's an old man in the corner, talking to 
   himself.  He looks up and smiles at you.  He says: 'Guys, I need your help.  
   There's a monster in the next room and I need you to kill it...'"
Fighter: "Does this guy seem trustworthy?"
Me: "Roll Sense Motive."
Fighter: "Um, 7."
Me: "He's not obviously lying as far as you can tell."
Paladin: "I use detect evil!"
Me: "You're catching some very faint evil.  It doesn't seem like this guy is
   personally evil -- he's certainly not been using any evil magic -- but he 
   might have been exposed to something evil recently?"
Bard: "I roll Sense Motive.  I got a 28.  Does this guy still seem trustworthy?"
Me: "No, he's totally lying.  There's someone in the next room and he's hoping
   to convince you it's a monster so you attack without talking to it first."