If anyone wants some help starting this should work for you as so many appear to be giving up quickly (there maybe better solutions, this is just one).
Your assistant choice doesn't really matter. A lower priced one earns you money faster but a high priced one gives you faster progress with some extra benefits later on.
Choose Binna, Roxy (Roxy should get to class A quickest) and Irene as waitresses.
Max the prices to plus 50% as it reduces the wait time (a lower wait time is very important) and increases revenue
The 2nd shift busier is than 1st and Fridays and Saturdays are the busiest days, so schedule accordingly
Use the pause plus button in the bottom right hand corner to max the speed to very fast to reduce boredom. (Then play another game / do something else and have this running in the background as it runs through each day but check progress often to look for booty calls scenes in the larger café and check progress.)
Only add one waitress at a time. Don't fire them as they restart at their basic rating / zero for class and xp, losing any progress made.
Wendy is the best 4th pick waitress when you get the 2nd shift. Later when you have the large café Tara and Brenda are excellent long term picks to fill in schedule gaps and will rise in class quickly when you go to large café and add dancers (attr - attractiveness matters in progress as the customers buy more from higher attr girls - don't choose Evelyn for example as she has a higher starting class but low attr which means her progress is slower) .
The aim is to promote the girls class from F-A asap to progress the game. To do this control the served % with good scheduling. Max progress with waitresses is made with the served percentage at 50-90% (plus the green smiley face). This increases xp and therefore the profitability index and the girls class. Under 40% reduces rating, money and customer satisfaction. 100% increases money quicker and customer satisfaction but slows girls progress as they are waiting around idle and not earning money.
Click on the girls in the bottom left hand corner as the appear in the larger café for additional sex scenes (booty calls)
Review all the girls each Monday so you can work out the schedule by reducing idle time (try not to fire them) and understand xp and class progress
Waitresses = progress & Dancers = money, so the focus should be on the waitresses, as the money will come with time.
It takes around 3-5 weeks to get to the larger café and 7-10 to get to the dancers.
Don't buy security as it slows progress massively when you have a third shift as its harder to get the customer satisfaction to 7.0.
I hope this helps as when you know what you are doing it makes the game a lot more fun. However as others have said the game desperately needs more scenes with the girls and more and varied dialog to liven it up and keep you interested. It has potential if they listen to the reviews, add some quality interactions with the next updates and possibly help players at the start so they don't give up quickly.