Service our customers? or Provide service to our customers?

INCORRECT		CORRECT
	My responsibility is to service our customers.		My responsibility is to provide service to our customers.

It is awkward to say that someone "services another person". Maintenance people can service machines. When people service other people, "service" takes on a sexual meaning. To use "service" properly in the above sentence, use the verb "provide".

Bring back memories.

INCORRECT		CORRECT
	I hope the photographs I took will bring you a great memory.		I hope the photographs I took will bring back memories.

The word "bring" would suggest something has been physically given to you. "Bring back memories" is an exception and is a set phrase in English. However, "provide" can suggest that something enables you to get something else. You can also say "I hope the photographs I took will provide you with great memories".

in local? or locally?

INCORRECT		CORRECT
	Our company sells its products in local.		Our company sells its products locally.

"In local" is incorrect as "local" is an adjective. You can say, 'in local markets" as "local" modifies "markets". You can also use "locally", the adverb, because it modifies "sells".

Knock? or Knock on the door?

INCORRECT		CORRECT
	I didn't hear you knock on the door before you came in.		I didn't hear you knock before you came in.

"Knock on the door" is grammatically correct, but sounds awkward. "Knock" is the correct and natural word choice. "On the door" is understood in the context and is therefore redundant.

by hands or by hand?

INCORRECT		CORRECT
	I usually wash my clothes by hands.		I usually wash my clothes by hand.

"By hand" is a fixed expression indicating how something was made or is done. You can also say "hand-made dumplings".

Eye contact

INCORRECT		CORRECT
	He rarely makes eyes contact as he is very shy.		He rarely makes eye contact as he is very shy.

"Eye contact" is a fixed expression. Similar expressions that use singular "eye" include "eye sight", "eye catching", among others.

High Peak or Peak?

INCORRECT		CORRECT
	Our sales reached a high peak last year.		Our sales reached a peak last year.

In "high peak", "high" is redundant as "peak", a noun, implies "a high point of something." Another sentence could be "Our sales peaked last year." Note that peak can be both a noun and a verb.