It's been said, but at rank 10+ you'll find that you're going to need all the help you can get in doing a craft "at your level" - for example just because you're a rank 10 blacksmith doesn't mean you can make rank 10 recipes with ease (far from it, actually).
Get the weapon that's closest to "Optimal" for your rank
Get crafting gear - anything with +Contol, +Output, +Craftsmanship and +Magic Craftsmanship. I think Control makes you keep the globe/elements stable, Output increases average progress per synth, Craftsmanship increases quality per synth, and magic craftsmanship reduces durability loss per synth (I could be way off on that, though).
And last, use the facilities buffs.
Got a source on that info on Output, because Output is a stat you have when you are a harvesting job (much like Control, Craftsmanship, and Magical Craftsmanship are crafter stats, Output, Perception, and Gathering are stats when you have a harvesting job).