Rewatch the first two OVAs.
Then Dual! Parallel Crisis Adventure, it's like Evangelion filtered through Tenchi.
Then OVA 3 or GXP, they're interchangeable here, but watch both.
Then Isekai no Seikishi Monogatari, about Tenchi's little brother. You could also just skip right to this, it's pretty standalone and it's why I still have faith in Kajishima after OVA 3 being lackluster at best.
Then OVA 4.
Or after the first two OVAs, you could watch Universe and the movies. Different continuity and character interpretations, but still fun.