Below is a list of frequently appearing idioms on the gmat. It is a list of 40 idioms divided in 4 sets of 10 for easier viewing and comprehension. While this list is not exhaustive, it provides a good few examples: :

1) To exchange X for Y (exchange X with Y or any other form is incorrect)
2) Different from one another (Different one from the other is wrong)
3) X is unknown, nor it is known - is a correct idiom (Neither is not required) It is not that nor would always be preceded by a neither
4) To ratify (At ratifying is incorrect) An attempt to ratify is the correct use
5) Allergy to (Allergy of, allergy for are incorrect)
6) To try to fix is the right idiom (to try and fix is incorrect)
7) Just as... So too
8) X is different from Y (different than Y is incorrect)
9) Same as X..as to Y e.g Gravity will apply the same to an airplane flying in air as to a ship floating on water.
10) From X to Y (Grow from 2 million to 3 billion) (From X up to Y is wrong)

11) Estimated to be (Estimated at is incorrect)
12) Believe X to be Y
13) Acclaimed as is the correct idiom (Acclaimed to be is wrong)
14) Distinguish between X and Y
15) In an attempt to (gain control)
16) Worried about (When talking about someone's condition)
17) Attempt to 'do something' (Attempt at doing is incorrect).
18) Both X and Y (Both X as well as Y is incorrect) Both at X and at Y is correct. Both on
X or on Y is correct. Both should always have parallel forms associated to it.
Similarly, 'Neither... nor' should have parallel forms associated to it.
19) Adverb twice cannot be an object of proposition 'by'. 'Increase by twice' is incorrect; 'doubled' is correct
20) So X as to be Y (So unreal as to be true)

21) As much as (Republicans are involved as much as Democrats).
22) X prohibits Y from
23) x forbids y to do z
x prohibits y from doing z
24) Credit X with discovering Y (Credit with doing something)
25) Credit X Rupees to Y's account (When money is involved)
26) Given credit for being ones...who
27) Believed to have
28) Regarded as having
29) Regarded as ones who have
30) Concerned for - worried; concerned with - related/affiliated

31) No sooner...than
32) X expected to Y
33) Mistake X for Y
34) Not X; but rather Y
35) Persuaded X to do Y
36) So X that Y (So poor that they steal)
37) Require that X be Y (Not require that X is Y)
38) As a result of
39) At least as strong as...(At least as great as)
40) Modeled after