I beat Level 10 awhile ago but I'm pretty sure this was how I beat it:
1. Make sure you always have flowers on every table-those extra points may seem trivial but really make a difference. Whenever a customer leaves, put fresh flowers on that table before seating the next-in-line.
2. Look for the customer with the least amount of hearts and give them  the drinks. Always use the drinks, because  they can change a customer's mind about ordering dessert or not and the dessert points are quite necessary!
3. BE CAREFUL ABOUT YOUR SEATING ARRANGEMENT!! DO NOT seat any of the teens, families, or men on cellphones near the book readers or aregular customers. They get VERY angry and will leave, which is a deduction of points. If you must, then be ready with frequent drinks to give to those unlucky customers next to the talkers.
4. Watch how long the line is. Try to stay near tables if the line is getting long. This puts pressure on the customers to hurry u and if ABSOLUTELY NECESSARY, don't give them dessert. You will lose more points by cutomers in line too long leaving, while not serving dessert simply doesn't ADD points on. Not serving dessert doesn't deduct any points at all. And remember what I said in ste 1 about the flowers!
5. MOVE FAST!!!!!!! YOU MUST BE SPEEDIER THAN A SPEEDING BULLET TO GET TO THE TABLES, CLEAR THEM, THROW DISHES AWAY, PUT FLOWER DOWN AND SEAT CUSTOMER.  WHEN YOU TAKE AN ORDER, GIVE IT TO THE COOK. DONT WAIT OR THE CUSTOMER GETS ANGRY AND GIVES LESS OF A TIP. THESE TIPS ARE VITAL TO YOUR WINNING! USE THE TIME WHILE THE FOOD IS COOKING TO DO OTHER THINGS!!!
 
Hopes my 5 steps program helps!!!
good luck!
Your eternal-ally in the Diner-Dash (Hometown hero) world,
Your fellow Diner-Dasher: roxy_surfer_gal_182