I park half of my forces in Teluch, in Armenia Minor(this half is from eastern Greece, Anatolia, and Armenia), and the other half on boats(this half is from western Greece + islands and Bulgaria).
The AI will take a county or two before making a run at your forces in Teluch, make sure you have good generals leading your troops. When they attack it will be over a river and into mountains, giving them a penalty and you a bonus. When the battle starts send the forces on the boats to join in. You should win that fight, so use your army to chase down theirs until it is nearly wiped out(<2000 left) then take back whatever holdings you lost. Don't finish off the enemy army completely until it is the only thing you can do to increase your war score, the AI won't dismiss the levies in it and re-raise whatever new recruits are waiting in it's territory.
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If you can make them surrender you will get a lot of money, bankrupting the Seljuks for years, and usually the emirs in de jure Armenia, Syria, and northwestern Mesopotamia will become independent, making great targets for quick expansion.
And for the Fatimids: try to get an alliance with the king of Abyssinia, when he calls for your help in repelling the inevitable invasion hit them hard. If you can take their holdings faster than they can take Abyssinia's you may be able to get them to surrender to your ally, bankrupting them enough to make them vulnerable to your own attacks.
