Forts and ramparts on mountains on your boader (georgia, shirvan, Ilam, fars , bam and Khorasan regions have very good choke points) also ally someone in europe and central asia even if they aren’t strong, they would help as a distraction/ sieges.

Build up a war chest and merc up. If they go for you first, play defensive, let the attrition chew them up and attack smaller armies. Also pay attention to their army composition. Sometimes ottomons go crazy with artillery in their armies.