Hmmm. I haven't had any problems surviving as the Byzantines (at least for the first 40 years), and I usually don't do the Exarchates / Viceroyalty Kingdoms until I'm close to my vassal limit.
Now, I do have quite a few playthroughs that I trashed early because something didn't go the way I wanted ("No vassal, *I* want Cilicia, and I don't want to have to revoke it from you"), although I've learned my lessons from them.
1) Don't have your Emperor command troops unless your succession is rock-solid. Or you want to kill your Emperor. Try not to risk your heir, either. It's not foolproof, (your heirs can still be stupid, my next-to-most-recent Emperor on my current playthrough buried all 4 of his children before himself dying at 71, passing the succession to one of his grandsons), but you want to minimize the risks.
2) I haven't really had to go into seclusion at all, although I haven't had a game go long enough for bubonic plague to make an appearance. (I keep restarting for various reasons, like "Oooooh, new expansion, I want to play through the whole game with this expansion!". Or "Dammit, I fscked up my succession.")
3) If you have word of an assassination plot against you, if you don't succeed in imprisoning the plotter and they run off, don't ignore the plot. They might get lucky. RIP Empress Anthousa.
4) Be conservative with war declarations, and don't be afraid to declare a white peace. It's cheaper than surrendering when you didn't commit enough troops initially, and it'll take too long to bring more in. Or a more urgent situation arose.
5) When declaring war, if at all possible, get in the first shot quickly. Retinues (although they're expensive to replace) and mercenaries (who are expensive to hire) are great for this. But expensive. But it can be much, much faster (and not pissing off your vassals) to park 6-10k mercs+retinue across the border, declare war, and then go to town.
6) Getting rid of Konstantine V's Zealous can be difficult. Scholarship Focus (if you have Way of Life) so you can Build An Observatory can be a big help, but it's not a guarantee. That being said, Iconoclasm isn't bad (it will become mainstream if you give it enough time), although you can't mend the Great Schism as an Iconoclast.
7) Get as many matrilineal marriages as you can. More dynasts that way.
Now, I do have quite a few playthroughs that I trashed early because something didn't go the way I wanted ("No vassal, *I* want Cilicia, and I don't want to have to revoke it from you"), although I've learned my lessons from them.
1) Don't have your Emperor command troops unless your succession is rock-solid. Or you want to kill your Emperor. Try not to risk your heir, either. It's not foolproof, (your heirs can still be stupid, my next-to-most-recent Emperor on my current playthrough buried all 4 of his children before himself dying at 71, passing the succession to one of his grandsons), but you want to minimize the risks.
2) I haven't really had to go into seclusion at all, although I haven't had a game go long enough for bubonic plague to make an appearance. (I keep restarting for various reasons, like "Oooooh, new expansion, I want to play through the whole game with this expansion!". Or "Dammit, I fscked up my succession.")
3) If you have word of an assassination plot against you, if you don't succeed in imprisoning the plotter and they run off, don't ignore the plot. They might get lucky. RIP Empress Anthousa.
4) Be conservative with war declarations, and don't be afraid to declare a white peace. It's cheaper than surrendering when you didn't commit enough troops initially, and it'll take too long to bring more in. Or a more urgent situation arose.
5) When declaring war, if at all possible, get in the first shot quickly. Retinues (although they're expensive to replace) and mercenaries (who are expensive to hire) are great for this. But expensive. But it can be much, much faster (and not pissing off your vassals) to park 6-10k mercs+retinue across the border, declare war, and then go to town.
6) Getting rid of Konstantine V's Zealous can be difficult. Scholarship Focus (if you have Way of Life) so you can Build An Observatory can be a big help, but it's not a guarantee. That being said, Iconoclasm isn't bad (it will become mainstream if you give it enough time), although you can't mend the Great Schism as an Iconoclast.
7) Get as many matrilineal marriages as you can. More dynasts that way.