How do you level crafts?

[tymora]

I leveled all my crafts at the same time, so I always have 8 leves to do from the same city no matter what.
You can do this when you do all the crafts with guilds in the same city.

[YUGON]

Usually, I use a thing called "recipe" -_-

[Gramul]

By doing them over and over without any great changes.
Doesn't that sound like fun?

[Len]

I leveled Alchemy & Fishing in tandem so that I could always supply myself with what ever fish I needed.

If you want to progress steadily while being able to provide your own materials, this is the path to take.