phil500 said:
1) am i forcing it if i pull the cler and pally aside and say a bit about why they should distrust the warlock?
Forcing it, and even ruining it. Don't invite your players to fight among themselves.
If the paladin's player is a fairly decent roleplayer, he will catch on to this on his own, and maybe even roleplay it well without destroying party unity. If he isn't a fairly decent roleplayer, then telling him not to trust one of the other characters is basically handing him the loaded gun and giving him a motive.
Bad idea.
What I would do is strongly encourage the warlock to imagine himself as a fallen hero of sorts, trying to be a good guy and throw off those chains of evil warlockiness. Sure, it's old hat, been done before (shades of Drizzt), but at least it justifies him being heoroic rather than dastardly.
phil500 said:
3) Should i RP the monsters in combat, as in, a buncha kobolds would likely think the guy with the big sword is the real threat, but a dragon would be smart enough to worry about the warlock 1st.
4) how should i convey to them they need to use tactics?
Monsters should always be played as if they were living, breathing creatures (except when they're not) with goals, ambitions, dreams of their own (unless they're mindless), who will do everything in their power to survive and/or win the encounter.
This means they will always use their best abilities as much and as effectively as they can. Even a dog would rather bite than scratch, and even a dog goes for throats and genitals as perferred targets. If a dog is that smart, then figure any monster as intelligent as a dog will use it's best abilities to their best advantage.
Monsters will set traps, lay ambushes, choose advantageous terrain, play for home field advantage, focus fire, gang up, overpower and overwhelm anyone and anything they can. And when the monsters are losing, they will pull out all the stops, drink their potions, use their emergency supplies, and go all out to regain the advantage. And when all that fails, they will flee or surrender and hope to survive to start a new life somewhere else.
Of course, not all monsters are like this. Mindless or otherwise extremely stupid monsters just bash away until they are destroyed. Some monsters are controlled by something else, such as a necromancer controlling undead, and even if the controlled monsters are intelligent, their actions are dictated by their controller, who may not care at all if they survive - but he will still want them to win so he won't have to face the PCs himself.
Ultimately, if you do everything you can with your monsters to utilize every tactic they are capable of using, it won't be long before your players are utilizing the same tactics.