Allied Seals
find a couple LS and go with them, also do daily and weekly hunting bills since it also give you seals.
if you consider using allied seals to gear up your character, put accessories on since they cost less than clothes
once you hit ilv80, you can farm TOS by running dungeons over and over.
as for allagan tome of Sol and Poe
since you just got to 50 and yet to finish MQ, I'd suggest you do the following
Dungeon: Sastasha (Hard)
Quest: It's Definitely Pirates
Location : Mor Dhona (X:22 Y:8)
NPC: Bloezoeng
Requirement: "The Ultima Weapon" main quest
and
Dungeon: The Sunken Temple of Qarn (Hard)
Quest: The Wrath of Qarn
Location: Mor Dhona (X:22 Y:8)
NPC: Hugubert
Requirement: "The Ultima Weapon" main quest and completed "The Sunken Temple of Qarn"
These 2 Dungeons will give you 40 Tome of Poe alongs with 50 Tome of Sol
but ilv requirement is 80, so if you haven't geared up properly, I'd suggest you go do some "hunting", since you can exchange ilv100 gears from Allied seals as well.