The faster you make the drinks, the more tips you get. Make the drinks in sets from right to left, not randomly - start making the drink closest to the bell, and work your way to the left.
From the walkthrough:
The ticket in picture form is placed on the top of the bar.
There will be 2 drinks per ticket.
The recipes to mix the drinks are found in the book at bottom left.
The drinks are made by placing the silver mixing glass under the juicer or the beer tap.
Then press the appropriate item's button as many times as the book says.
If the mix needed to be blended, a picture of the blender is seen in the book.
Place the solid ingredients first in the blender and then press the blender button.
Place the serving glass on the gray mat and pour the mixed-blended drink on it.
Place the drinks on the plate beside the ticket on top of the bar.
After doing the 2 drinks in the ticket closest to the bell, press the bell.
If a mistake is done discard the drink at the rubbish bin at bottom right.
Do the mixing fast and proper and get more tips.