If you are just starting or wondering what workers should you hire try considering this.
When hiring workers you have the chance to choose between grades ( Normal, Magic, Rare, Unique, Epic) but you'll be lacking contribution points. It doesn't matter if you hire a worker with a lower grade because you can upgrade that worker with the same contribution points that you'll be spending when hiring, and in max level (which is level 50) they will all have the same stats depending on their specialty.

These are the things that you should consider when hiring:
Vitality - workers with higher vitality can collect resources faster when gathering and consuming low food.
Strength - workers with higher strength can build faster and consume low food.
Dexterity - workers with higher dexterity can craft or create products in your camp faster and consume low food.

What to Hire First?
When choosing which worker should you consider hiring first try to hire a worker with higher strength because you'll be needing him/her to build things in your camp faster. You'll be needing at least four with higher strength because they will be of no use when you already max out everything.

Workers in Merchantry and the Sailors
In merchantry, it doesn't matter what specialty the worker has what matters is their level, but when considering what worker should be in there try putting workers with higher strength. Workers with higher strength become less of use when you max out everything, they gather and craft much slower (depends on their sub-specialty). That is why they are most efficient in just doing merchantry.
In sailing in the Great Ocean you'll be needing a max of seven workers when you already upgrade your ship to the higher tier. Try to avoid putting workers with higher vitality because you'll be needing them gathering every day. You should consider making sailors who are not much of use when gathering thus the worker with higher strength and dexterity. The four sailors should also be the ones that you use in merchantry because you'll be needing their attack when fighting Pirates in the Great Ocean. The three sailors should be the extra crafters.

Gathering Workers and Crafters
When gathering just consider dividing them in foraging, mining, and logging because when you already have a master in life skill you'll be needing to at least have your workers gather in these three regions to have a rare find. You should have at least 24 workers that gather and all of them should have higher vitality. Assigning workers always depends on what resources you need but if you don't need certain resources just divide the workers in these three fields to maximize your resources.
The Crafters are workers that have high dexterity and you should consider hiring a total of eight of these. They are also the same as your builders that become much less of use in the later time ( if you are considering crafting cron stone you'll end up lacking food which isn't efficient because you'll be needing food doing merchantry, I suggest buying cron stone weekly in Pearl Shop and if you doesn't have enough Black Pearl remember that Merchantry gives Black Pearl). Make the three crafters as your sailors if you aren't using them and the other five crafters will only focus on crafting the X-Large Stamina Potion (this potion is vital in-game you'll be thankful that it can be crafted now.)

Final Tip in Workers
The maximum number of workers that you'll be having is 36.  In which 24 workers have higher Vitality for gathering, 8 workers have higher Dexterity for crafting and 4 workers have higher Strength for building. There should be Sailors consisting of the 4 that do the merchantry and 3 that is extra crafters.
Bonus Tip: To avoid confusion try naming your workers depending on their specialty Eg. Gather, Crafters, Builders etc.

Dandelion
Chowpan

Can you explain how contributions are earned? Not accumulating any at thisnpoint.