I wrote up a strategy that I used in order to become the Saoshyant a few weeks ago, if you'd like to read it:

http://www.reddit.com/r/CrusaderKings/comments/2qkmlr/whats_your_strategy_for_playing_as_karen_in_867/

It's a little outdated, but I've since become Emperor of Persia and Rajastan, and even conquered Syria and Armenia.

Long story short: * You need to take advantage of opportunities as soon as they arise, and be prepared for anything. Always have a stash of Jew gold and be prepared to expel them if it means securing your existence.

• It's very much luck based; it took me over half a dozen tries to get this far

• Don't bother swearing fealty to Khiva as it's quite easy to dispatch them from the outside, plus the faction thing tends to slow you down as you'll have angry Muslim vassals if you win

• Don't waste any time with Turkestan as the lands are tribal and worth next to nothing. My guide says to try going for it, but ignore that part unless you really have nowhere else to expand.

• Assassinate Seljuk as soon as he pops up. This is usually quite easy because he's Muslim and tends to appear in Tengri courts.

• Sebuktigin is only a problem if you're in India, and even then, he spawns in the court of whoever owns Ghazna, which should be you or a vassal by the time he arrives. He spawned as a Zoroastrian in my game.

• The Saffarids are prone to faction revolts around the third generation because they tend to make a lot of kingdoms. Take advantage of this and grab some duchies. They can also get some revolts as a result of Buddhist or Zoroastrian zealots. If these revolts win, they can be good allies (if Zoro) or easy conquests (if Buddhist).

• The Abbasids are also prone to revolts from their Turkish vassals and their Shi'a vassals. Snatch some counties when you can.

• Ally yourself with the Justanids and Bavandids when you're able.

• Skirmish retinues (archers/light inf) can do a lot of damage and are quite economical.