Incorrect: The car either dashed against a goat or a donkey.
Correct: The car dashed against either a goat or a donkey. (either + noun + or + noun)

Incorrect: Neither he would eat nor allow us to eat.
Correct: He would neither eat nor allow us to eat. (neither + verb + nor + verb)

The correlatives either…or, neither…nor, both…and and not only…but also must be placed immediately before the words which they relate to.

Incorrect: Though he was poor but he was happy.
Correct: Though he was poor he was happy.
Correct: He was poor but he was happy.

One conjunction is enough to join two clauses.

Incorrect: He asked that what was my name.
Correct: He asked what my name was.

Incorrect: He enquired that where was the office.
Correct: He enquired where the office was.

Students often make the mistake of using the relative pronoun that before interrogatives like what, where, when, whether and why.

Incorrect: Do it carefully lest you may not make a mistake.
Correct: Do it carefully lest you make a mistake.

Lest means that…not, and, therefore, it will be wrong to add another not in the following clause. It should also be noted that the only auxiliary verb that can be used after lest is should.

Incorrect: He climbed up a tree such as to get a good view of the procession.
Correct: He climbed up a tree so as to get a good view of the procession.

Such as indicates result. So as indicates purpose.