A lot

So many people write a lot as one word instead of two. 
If you do this, ask yourself if you would write alittle or afew. Of course not, right? So please don't write alot! 
For example:
There are a lot of blunders in this blog.
A lot of people will attend the event.

Back

Do you use expressions like return back or exchange back?
If so, you don't need the word back – it's completely redundant!
For example:
I must return the shoes because they are too big.

Compare to/Compare with

When comparing things that are dissimilar, use compare to.
When comparing things that are similar, use compare with.
For example:
My life has been compared to a soap opera.
Ripples on the water can be compared to frosting on a cake.
US Congress may be compared with the British Parliament.
Compared with running, walking is better for people with knee problems.

Discuss

It is not grammatically correct to say discuss about.
The word discuss means to talk about, so if you say discuss about, you are saying talk about about.
The same applies when you use the word mention. We don’t need about.
For example:
Mary mentioned that her report was overdue.
I want to discuss the agenda for next week's meeting.
In Shirley’s workshop we discussed the new rules for effective writing.

Everyday/Every day

Everyday is an adverb.
Every day as two words are adjective and noun.
For example:
Making your bed is an everyday chore.
I get the bus to work every day.
Having to write e-mails is an everyday task.