Few Quick Tips

1. Do not use since with an amount of time. Use for.

• I have been here since six weeks - incorrect
• I have been here for six weeks - correct

2. Do not use the simple present in a sentence containing since. Use the present perfect.

• I am here since January 5. - incorrect
• I have been here since January 5. - correct

Look at vs. Look to

Look at implies to turn the eyes in a certain direction so as to see; to use one's sight.

• He turned and looked at her.
• I’d like a skin specialist to look at that rash of yours.

Look to (someone or something) implies To rely on, turn to or refer to them or it, to expect

• Children look to their parents for help.
• This looks to be a very difficult assignment.

Maybe vs. Probably

Maybe

adverb

written as one word, defined as possibly or perhaps.

used to indicate uncertainty or possibility.

• Maybe it won't rain.
• Maybe no one will come to the party.
• Maybe you were right after all.

Probably
adverb

used to mean that something is very likely

• Sam was probably right.
• I'll probably be home by midnight.
• The infection was probably caused by swimming in contaminated water.

Economic vs. Economical

Economic is not same as economical.

                                                          

Economical means frugal, careful in management, not exaggerated or excessive; it has to do with saving.

• the most economical method

    

Economic means of or relating to production, distribution or management of wealth, pertaining to financial matters of a country or household. It means connected with the science of economics: relating to trade, commerce, the production and distribution of wealth, etc.

• economic problems
• a period of economic expansion.

Known to vs. Known as

Known to: when we want to talk about some fact that people have learned.

• Lions have been known to occasionally kill large beasts like elephants, giraffes, and rhinos.
• Elephants are known to communicate with seismics, vibrations produced by impacts on the earth's surface or acoustical waves that travel through it.

Known as: when we want to talk about the name of somebody or something or its definition.

• Some male Asian elephants are tuskless and are known as Muknas
• Lions are big cats known as the "King of the Jungle". 

Especially vs. Specially

Especially means 'particularly, to a degree beyond others'. To stress on exceptional quality, use especial or especially.

• He did especially well in national games. (A noteworthy performance)

Specially means 'for this purpose, or to this end, and no other'. To stress on the distinctive purpose of something, use special or specially.

• This laboratory is built specially for research. (A distinctive purpose)