I'll help out as much as I can. The quick and dirty is abyssea, abyssea, abyssea. BLM are absolutely vital for this, so you will never be hurting for a group. There are two primary reasons for this. First is for exp groups (which you will be starting out doing), because of the way lights work blm are ideal for building azure light, which is needed for time extensions (TE). I'll let you go to this page
and read up for yourself on how those work. Essentially, you kill stuff with magic to get more blue chests, which have a chance of being TE, which is good.
The second thing you will be needed for as a BLM is for empyrean gear farming. BLM is needed for the yellow proc which increases the drop rate of seals and other items that improve the stats on empyrean gear (think of it like the abyssea version of artifact gear). This page
will give you a rundown of the proc system. (Pay particular attention to yellow, but it won't hurt to know the others either.) Also, if you don't have your brd leveled to 50, get it there. BLM are expected to sub brd to cover an extra proc, specifically the threnodies (you will need to use elemental seal for them to be effective). So if you don't have brd yet, that should be high on your list of priorities.
As for gear, whatever you have currently is fine for now. At 78 you'll get access to the Teal set
, which will render most of your other gear obsolete. The other plus to this is that it is very easy and cheap to obtain (just buy with cruor if nothing else). Once you get into the 80s, it's time to start looking into the empyrean gear for blm, the Goetia set
. Now, that base gear doesn't look too appealing, I know. But this is because you have to take extra steps to improve the gear, which turns it into something really incredible. Follow the appropriate links to the +1 and +2 versions of the set, and you'll see what I mean. That is what I was talking about earlier with the yellow procs. You have to obtain Goetia seals from certain NMs in abyssea in order to get to the +1 version of each piece, then get more items to unlock the +2. I'll let you read up on the details yourself, but that should get you started.
Now, atma. That's a really long discussion that I don't want to get into, so I encourage you to use the wiki (This page
is long and detailed, but should have all the info you need) to look up the details. What I will tell you is which atma to focus on getting: Ultimate, Beyond, Minikin Monstrosity, Baying Moon, Merciless Matriarch. Those are going to be your top tier atma, if you see shouts for any of these, get in them. You can look those up on wiki as well to see how to get them. Do you have any other questions?