Hey! I've recently become a new entry to the full ZBLL club.
so, first of all, as DG said already full ZBLL is a huge commitment, make sure you really want to put in the effort for such a big task.
second: USE THE ZBLL TRAINER TO YOUR ADVANTAGE
it's helpful as heck, and helped me consolidate the first algs I knew.
remember this one thing: the more algs you know, the easier it is to learn others, because you get more used to it, and you're able to relate new algs to others more often, and for a big alg set this is VERY useful.
so, with that said, here is how I learnt ZBLL:
I created a bunch of txt files, one for every OCLL (you can use spreadsheets too), each of which the cases by COLL.
I indicated the cases by how they're indicated them on the ZBLL trainer, so I could just check the file and instantly know what
cases I should input into the trainer. so for the U case FBBF CxO, i would have it on the U file, in the FBBF (checkerboard) section, and i would write CxO. then I would write the algorithm, that I broke down into triggers using a teamBLD notation I saw somewhere (I think bob burton site). triggers include push=R U' R', pull=R U R', super=R U2 R', front-push=F' U F, back and left versions, and also wide move versions. I would write the algs with that notation, then train them.
The order I recommend is this: learn 2GLLs (order: T/U simultaneously, L, Pi, H, S/As, which can be delayed a bit), while making sure you know all COLL+skip cases for T, U, L and some mirrors and inverses as well. H, Pi and S/As+skip cases are harder to recognize, except for diag H.
next I recommend learning ZBLL for the worst U-set COLL (R' Y-perm R), and then finish the other COLL sets, while drilling them as soon as you finish a subset. meanwhile you can learn some other random T and L cases. next I would learn T and L, by starting with diag cases, because they're the worst. meanwhile learn easy cases. you can also learn some H/Pi/S/As if you want (I remember learning all sune+F-perm cases because I was into OH, and the COLL+skip cases+mirrors and inverses for all other COLL cases at this point)
finish with H, Pi, S and AS, again starting from Pi. (actually I learnt diag Pi after starting L, because diag Pi is so bad)