Beginner info will go here, other helpful links in the post below.
Official Strategy Site
FFRK Reddit - "Newbie Guide"
FFRK Reddit - FAQ
Save all your gear at the start and combine it to get at least 3 star gear for as many realms as you can. Some items off the top of my head: Kunai (IV), Bronze Helm (V), Mythril Helm, Dagger (IX), Bronze Helm (II), etc. There are also a few pieces of 4* gear you get as rewards for completing dungeons. Diamond Helm, Light Rod, Light Staff, Killer Bow, a Harp, and maybe a few others.
Synergy adds 10 levels to a character from that realm and gives increasing gains the higher level the equipment. There are ranges for the gains, though. I think it's something like 1-5, 6-10, 15-20, or so where anything in that range gains the same bonus. In order to gain more it has to go to the next tier.
At this point in time. Complete a fair number of regular dungeons, then try to get through the two current events if you're able to get your guys to around level 30. The event reissues do not come around too often, but they do add characters back in after a bit by completing Bonus Quests which can be viewed in the Realm screen then hitting Dr. Mog in the top right Quests icon.
Along those lines, I strongly suggest you keep up with your dungeon quests so that you do not have to go back and repeat dungeons a second time. Make sure you also check out the ability quests you have available. A lot of times the quests will reward you with the full amount of one of the types of orbs you needed to complete the creation or honing of that ability.
Honing is very important as you're probably realizing. You only have a certain number of uses for an entire dungeon and Ethers do not drop often enough to rely upon them. In the later stages you'll gain Record Materia that allow your Black, White, and Summoning magic spells to be recharge between each stage, however rationing is still important. When you've got some more time in, and you're going to start challenging the boss rushes, ability uses is going to determine what you get out of the event. You could refresh ability uses by using Mythril, but you wouldn't want to do that for each battle because it's just an overall loss. You also should not heal between stages using Mythril. If it's really that critical that you beat a given boss, but you're out of ability uses, the best option is to let your party KO and then use a Mythril to refresh. By doing so you will get your abilities refreshed, all characters healed, and also gain an additional buff.
As far as abilities to hone, you're going to need a few of the basic abilities to get started before you can get too far in. This includes things like Blade Bash, Jump, Thunder/Fire/Blizzard, Cure, etc. I would generally say only hone these until you get to the point that you can complete the current content (for your level) so as not to waste gil and orbs on abilities you won't use later.
Some abilities that will last you a while: Dark Buster, Venom Buster, Double Cut (I have 2 of these at rank 4), Power Break, Armor Break, Magic Break, Mental Break, the -ga line of spells (this includes Slowga and Silencega), Tempo Flurry, Faith, Spellblades (Fire Strike, Thunder Strike, etc as well as their -ra tier), and Intimidate.
That seems like a lot, but you'll work through it between the classic dungeons and the daily dungeons to get the orbs you need for each ability. Do not worry about 4* abilities and Summoning magic just yet. In order to get most of the 4* and higher orbs you'll be completing events and elite dungeons or farming specific fights for drops. 4* orbs can also drop during the daily dungeons, but some people have more luck than others. I generally don't walk away with too many 4* orbs on any given day; maybe 3-4 at most.
Party composition is pretty standard. I generally take 2 strong melee, 1 support character (to use breaks, dark/venom busters, etc.), a WHM, and a BLM. As far as characters to level; Cloud is a good all around character. He can use spellblades, combat abilities (breaks, double cut) and has one of the higher ATK stats. Zack is pretty much the same as him. DRK Cecil is a strong physical attacker, but can't use spellblades. Sephiroth is the same. Wakka and Tidus are both good attacker/support characters and I believe they are both available through Bonus Quests. You'll also want to level Black Mage, White Mage, and Summoner up to 50 eventually to gain their Record Materia that refreshes the relative spells.
Don't be discouraged if you can't complete whole events at this point. Try to get the characters if you can, but if you get stuck you'll spend your time better honing abilities and level your party than you would banging your head into an event above your means.
I guess the last thing for now would be Roaming Warriors. Try to get some good friends that have buffing abilities. Attack Soul Breaks are good as well, but I find myself using buff abilities 99% of the time. These would include Stoneskin II, Sentinel's Grimoire, Boon, Lunatic High, Hymn of Fayth, Advance, Runic, etc. Things to avoid: Single target attacks and default SBs (the ones that are automatic for that character).
That's all I've got for now.
A couple things to note; there are a lot more characters now and tiers have been changed up a little.
Cloud, Squall, and Sephiroth are all capable (or will be in the next two days) of going up to lv 80. In addition to them Paladin Cecil, Rinoa, Tyro, and Tidus will also be able to break their 65 cap soon. Lenna is also due to get the cap break in a couple weeks as well.
As the summary above says, check out the "Quests" menu and start going through the basic "Complete XXXX" stage quests to get some Mythril, eggs, etc. Also make sure you check that menu before making abilities to take advantage of orb and Mythril rewards from those quests.
The Bonus Quests tab can net you some of the characters from past events. Lenna, Squall, Tidus, Paladin Cecil and the others I mentioned above should be priority to get.
Depending on how you're doing, there are a good number of characters in the current Sephiroth event that you should be able to unlock if you have a full party about lv 30. Make sure you have a decent stock of stamina, though, in order to be able to complete the events. Each stage could take 20+ stamina to complete so you should make sure you have at least 30-40 (also for sanity purposes).
Stamina refreshes every 3 mins so you get 20 stamina an hour. Checking the game every hour can be a pain in the ass so higher amounts of stamina are always useful.
Going to end there because it's already a wall of text.
==== Forum Threads ====
Equipment you might want - Really in depth write up about a lot of 5* relics
==== Spreadsheets ====
Dungeon Updates (Current & Future)
- JSON data of all abilities and SB's
- c_en is for "Counter_Enabled." A value of 1 means it is able to trigger an enemies counter. A value of 0 means that under normal conditions, it will not
- Record Dive data for all characters. (Record Dive is not available on Global yet)
==== PDF's ====
Happy Pluto PDF - Tons of good info here.