Natural allies:Baratheon:Greyjoy
Lannister:Stark>Martell
Stark:Lannister>Tyrell>Martell
Martell:Lannister>Stark>Greyjoy
Tyrell:Stark
Greyjoy:Baratheon>Martell
Usually you don't need too much talk with them cause they are born to be your friends and they may help you a lot.For example,we can rarely see Bara-GJ alliance,but it's rather strong.GJ goes north and Bara helps him in track positions and attack Lannister.When the chance comes bara goes north and they can divide the north by sea:GJ taking moat calin,Winterfell and Bara taking the rest.(It relies on a southern fight)
Other strong natural allies:Stark-Lannister aginst Greyjoy;Bara-GJ allliance against Lannister;Lannister-Martell alliance against Tyrell/Baratheon
Potential enemies:Baratheon:Lannister=Martell=Stark(speacial cause you usually win by attacking him but he's not very threatening to you)>Tyrell
Lannister:Greyjoy=Baratheon>Tyrell
Stark:Greyjoy>Baratheon
Martell:Tyrell>Baratheon
Greyjoy:Stark>Lannister>Tyrell
Tyrell:Martell>Baratheon=Lannister>Greyjoy
It's clear that everyone has at least 2 potential enemies so everyone needs to negotiate.Baratheon,Lannister and Tyrell extremely need diplomacy.Even if the houses in corner,such as Stark and Martell if you are teamed up against its hard to defend and no one else can save you because of your position.
It's very ideal to ally with your potential enemies in the 2nd/3rd position I listed against your main enemy(For example,a Bara-Tyrell alliance against Martell is rather desirable although very uncommon).You stop others from teaming up against you and have one enemy against another.Having peace with your biggest enemy is also a choice here,but I usually look for chances to betray unless I find some other spots.For example, if I am Martell and there is a boring peace in south.I usually wait for Tyrell attacking GJ/Lanni/Bara,leaving his sea not well defended.Then a doran and an attack on sea makes sense.(Unless I have broken through Bara sea before that)
Welecome for your ideas about this.