The only thing I really did in version 1.0 was fishing, so I started game as a level 23. I went to the fisherman's guild and picked up my lvl 1, 5, 10, 15, & 20 quests (not all at the same time of course) and did those and just by fishing a little bit to finish those quests, the next thing I knew I was level 25.
From that point I still had a bunch of rested xp from phase 4 beta to early access.
I went to Costa Del Sol and fished till level 30 and then Moondrip (just North of Vesper Bay) till 35.
After that, it is dunefishing from 35 - 40. Then I went to Burning Wall in Eastern Thanalan from 40-45. Then finally capped it off with skyfishing from 45-50.
I pulled a marathon grind from 38-50 in about 14 hours (including the lvl 40, 45, 50 fishing quests) and about 2 hours of profit fishing.
I got lucky and made some very good profit fishing as soon as early access began, but now the undercutters have already saturated the market. I am still making some gil... but in the first couple of days it was very very nice.
Edit: It is very important to spend the gil to buy good perception gear. It makes it a lot faster to level up when you are pulling in HQ's frequently for 14k - 20k per fish instead of 2.2k - 4.5k per fish.
Edited, Sep 3rd 2013 2:59pm by LordMethos