So after some more experimenting I am pretty confident that experience overall is 50% (towards your character level) and Skill Experience is 75-80% for Lives that do not naturally have the Skill you are using. Interestingly enough crafting experience is not affected by the quality of the item you create. A Superior item nets you the same experience and skill experience as a normal one. EDIT: Combat skills below.
I will post the numbers I have later.
As a Blacksmith:
* "Good" Gold Pickaxe - 115 exp - 215 Smithing Exp
* "Good" Iron Sword - 25 exp - 71 Smithing Exp
* "Great" Iron Sword - 25 Exp - 71 Smithing Exp
As a Carpenter:
* Normal Gold Pickaxe - 57 Exp (50%) - 170 Smithing Exp (80%)
* "Great" Iron Sword - 12 Exp (50%) - 55 Smithing Exp (76%)
Combat Basic data. 33% Experience gain for a skill not naturally used by that Life.
As a Paladin:
* 3 hit combo on Pterodactyl - 15 Longsword Exp
* 2 Hits (one each on the sheep things in East Grassy Plains) - 6 exp
As a Mercenary:
* 3 Hit combo on Pterodactyl - 6 Longsword Exp (33%)
* 2 Hits (one each on the sheep things) - 2 exp (33%)
As a Blacksmith:
* 3 Hit combo on Angry Cactus - 6 Longsword Exp (33%)
Not sure how much more in depth I want to go. But I was very surprised how low the combat exp was for the wrong Life. And it looks like being a crafting job does not change the ratio.
The time used to catch the fish is not relevant because the fish is chosen by the game when you first pull your rod, hence the HP bar becomes easy or difficult to pull.
Each area has like 3-4 types of fish, and maybe two of then can be caught in giant size.
And to be better at fishing you just have to fish a lot and in tougher places, so you can level up faster.
Best Answer
Improve your Focus and Dexterity and some high quality tools is the way to go.
There is no secret to this, always use the life level tool (lvl 2 cook with silver frying pan, etc) and put some points in the main status of the life.