Things I Wish Someone Told Me Earlier

Here is a partial list of things I had to learn the hard way...

Almost EVERYTHING is controlled by a level of one sort or another. Most equipment and magic can be used at or after certain levels. If your char has a skill (sword, elemental magic, leathercraft) these skills are controlled by their own levels separate from your "job" level. Skill levels only skill up in appropriate circumstances.

Many equipment pieces are further limited by job, race and gender.

DO NOT leave town without Signet. Also, make sure your Empress Band has enough charges.

Macros will make your life so much easier. So will keyboard shortcuts, especially:
Ctrl-T = Tell
Ctrl-R = Reply (to last person to Tell you something - press again for next person)
Ctrl-L = Linkshell
Ctrl-P = Party tell
(look into the others like A-attack, I-item, E-equip, M-magic, J-job skill, W-weaponskill)

If you're a mage, really think about "fighting" and "resting" gear sets - the fighting set should enhance the appropriate attributes (e.g. Int for BLMs, Mnd for WHM) and the resting set should maximize MP recovered while healing (MPR).

When in a party, you can pull up the map screen and see markers for party members on that map - but you have to scroll left and right through the marker categories!

There's probably more - for next time!