How to get past Level 26:

Round 1:

Sit the Joggers in the middle table, the Cellphone Addicts to their right, and the first two groups of Bookworms at the two tables above and below the Joggers.

Serve those four in combos.

Round 2:

Sit the group of six Business Women at the six-top table, the Joggers in the middle, the first two groups of Families in the top row, the Cellphone Addicts to the right of the Joggers, and the green and blue Bookworms at the remaining table.
(Let the yellow and red Bookworms go).

Serve those six in combos.

Round 3:

Sit the group of four Business Women on the bench while Round 2 eats. Once Round 2 is done, sit the green-red Cellphone Addicts where the previous two were, the group of six Young Ladies at the six-top table, the remaining Family group and the blue Cellphone Addicts at the top row, and the group of four Business Women at the table next to the six-top table.

Serve those five in combos.

Tip: Use the phone, bench, and drink station wisely.

Tip: Serve desert to the fast eaters if they earned it.

How to get past Level 31:

Round 1:

Sit the group of four Young Ladies at a four-top table, the group of three Cellphone Addicts at the other four-top table, and the group of two Cellphone Addicts at the two-top table up or above the group of three Cellphone Addicts.

Serve those three in combos.

Round 2:

Sit the group of six Bookworms at the six-top table, the purple at a two-top table, the blue-purple Young Ladies at another two-top table, and the group of four Joggers at a four-top table.

Serve those four in combos.

Round 3:

Sit the blue-red Cellphone Addicts at a four-top table, the group of six Cellphone Addicts at the six-top table, the Family at the other four-top table, and the green Young Ladies at a two-top table, above or below the Family.
(Let the group of three Bookworms go).
Serve those four in combos.

Round 4:

Sit the group of five Young Ladies at the six-top table, the green-blue Young Ladies, blue-purple Bookworms, green-red Cellphone Addicts, and the yellow Young Ladies at the four two-top tables, the group of three Young Ladies at a four-top table that's not near the green-red Cellphone Addicts.

Serve those six in combos.

Tip: Make color bonuses.

How to get past Level 40:

Round 1:

Sit the group of six Business Women at the six-top table, the green-red-yellow Business Women at the bar, and the yellow-green-blue-blue Bookworms at a four-top table.

Serve those three in combos.
Serve desert to those who have earned it.

Round 2:

Sit the group of six Young Ladies at the six-top table, the Kindly Seniors at the bar, and the green-yellow-blue-blue Cellphone Addicts where the Bookworms were.

Serve those three in combos.
Serve desert to those who have earned it.

Round 3:

Sit the red Young Lady, the red Business Women, and the blue Joggers at the bar, the green-blue-red Joggers at the six-top table (try to figure out the color bonus there) and the green-yellow Young Ladies anywhere but the bar.

Serve those five in combos.
Serve desert to those who have earned it.

Round 4:

Sit the green-yellow-green Family at a four-top table, the group of six Kindly Seniors at a six-top table, and the green-red Cellphone Addicts at a four-top table.

Serve those three in combos.
Serve desert to those who have earned it.

Round 5:

Sit the blue-red Book worms at the bar, the group of six Young Ladies at the six-top table, the green-blue-green Family at a four-top table, and the yellow-purple Business Women anywhere but the bar.

Serve those four in combos.
Serve desert to those who have earned it.

Round 6:

Sit the three remaining groups of people anywhere.

Serve those three in combos.
Serve desert to those who have earned it.

Tip: Use the phone, podium, and drink station wisely.
Tip: Make color bonuses.

how do you get passed level 30

How to get past Level 41:

Round 1:

Sit the group of five Business Women at a six-top table, the group of two Bookworms at a two-top table. Sit the Family and the group of three Joggers next to each other. Sit the group of six Young Ladies at the other six-top table.

Do everything in combos now.

Round 2:

Sit the group of four Cellphone Addicts and the Family next to each other. Sit the group of two Kindly Seniors at a two-top table. Sit the group of three Young Ladies and six Business Women at the six-top table. Sit the group of two Bookworms to the left of the six-top table.

Do everything in combos now.

Round 3:

Let the red Business Women leave. Sit the group of six Young Ladies and the group of blue Joggers at the six-top tables. Sit the group of two Cellphone Addicts at a two-top table. Sit the group of four Business Women, the Family, and the group of two Bookworms at the four-top tables.

Do everything in combos now.

Round 4:

Sit the group of six Young Ladies at a six-top table.
Sit the group of two Young Ladies anywhere.

Serve the two remaining groups of Young Ladies in combos.

There's a forum post that says "Level 30". It's got a post in there that may help you get past Level 30.

where

In the Diner Dash 2 forums, probably on the second page.

how do you get pass level 33 its sooooooooooooooooo hard for me

How to get past Level 47 (Part 1):

Round 1:

Sit the purple-blue-yellow Young Ladies and the red Bookworm at the bar. Sit the blue-purple Young Ladies at a two-top table and the red-green Young Ladies at another.

Serve those four in combos.
Serve desert to those who earned it.

Round 2:

Sit the purple-blue Cellphone Addicts and red-yellow Business Women at the bar. Sit the blue-yellow Cellphone Addicts, the blue-purple Joggers, and the green-red Kindly Seniors at the bar.

Serve those five in combos.
Serve desert to those who earned it.

Round 3:

Sit the blue-yellow Joggers and the red-yellow Joggers at the bar. Sit the two Familys at the two four-top tables.

Serve those four in combos.
Serve desert to those who earned it.

Be back later with Part 2...