Playing my first game as the Byz right now, once I got over the first attack by Seljuks which was a bit touch and go, I took Dwin to the E/NE without much bother, then went for Jerusalem.
Might be a little bit cheatsy but I loaded up my ships with half my army, sent the other half to take low 'Supply Limit' provinces on the coast, and once the big enemy stack came to take back said provinces ( losing their troops to attrition ) I'd land my other army to retake any territory lost, quickly and easily because of low garrisons

rinse and repeat if needed, not long before they are cut down to size. Then lure with one half on the coast, land the other as battle begins, then roll them over
Good luck mate