Hi ALLucK - and welcome to CivFanatics!
One strategy is to assess each city's 'fat-X' (workable terrain after a border pop) and determine your needs in terms of an empire, and the value of the city as a commerce city vs. a production city.
One thing that separates the human from the AI is that the human is allegedly better at city specialisation - and this is why many are dubious of the 'Automate Worker' function.
A city with a few hills and a river running through it tends to offer good

-yield possibilities and therefore a good unit pump. That is, the river provides fresh water for Farms, and these can support the

needs of the citizens working the mines in the hills. A coastal city with a couple of seafood resources may make a decent enough

-centre, and may not need a lot more food, so the land tiles can be cottaged for extra

, although
some 
is usually beneficial. These cities are good for boosting

and

output.
The role of your Workers will be to support those cities' roles. They must ensure that there is adequate

(Farms and Pastures) to support the city, but also deliver an optimum balance of

and

. Rather than having every city build every building, specialisation allows the player to get on with maximising the city's best role and not wasting

on superflous buildings for that particular city site. There are some buildings (e.g. Granaries) that will benefit both a

-oriented city as well as a

-oriented city.
See
Sisiutil's Strategy Guide for Beginners for further thoughts on specialisation, but to recap - the role of the Worker is in part to support specialisation of cities.
Note also that some improvements get better as new technologies and civics are embraced (e.g. Windmills, Workshops and Watermills)