Between is used to refer to two or more things which are clearly separated:

• Stand between the red lines.

Among/ amongst is used to refer to things situated more or less centrally in relation to several other things:

• There was a small cottage amongst the trees, deep in the woods.

[Amongst is UK English]

We use fewer with countable nouns and less with uncountable or mass nouns:

• We sold fewer cakes this month compared to the same time last year.
• The fewer words she says the better.
• We’ve got less money than I thought but I don’t know why.
• The less said, the better.

Less is normally used with numerals:

• She had a score of less than 100.

and with expressions of measurement or time:

• He worked here for less than two weeks.
• We live less than four miles away.

but fewer is used if the things denoted by the number are seen as individual items or units:

• There were fewer than ten candidates for the position.
  

We use:

• e.g. to mean for example
• i.e. that is to say and is used to add explanatory information or to state something in different words:

• There are many types of material from which shoes can be made e.g. leather, plastic, cotton.
• It’s a new type of shoe made from laboratory enhanced organic polymer, i.e. a synthetic leather.
  

Too means to a higher degree than is desirable, permissible, or possible; excessively; or in addition, also:

• I want to go too.

To is an infinity marker:

• I agreed to take him to the meeting.
• I need to go now or I will miss my train.

and a preposition:

• I walked down to the shops yesterday.
• We went to the train station.
  

When referring to a brand or entity, use it as using they or their can confuse:

• To keep up with their changing audience, Anderson & Cº rebranded in 2001. [confusing]
  

Their and they refer to people not a brand or entity. Therefore, when one refers to an entity rebranding, we use it:

• To keep up with its changing audience, Anderson & Cº rebranded in 2001.
  

Its is a possessive determiner to mean belonging to or associated with a thing previously mentioned or easily identified:

• We bought this house for its charm and space.

It’s is a contraction of it is:

• It’s wonderful to see you!

The confusion arises as some possessives do have apostrophes:

• The man’s house was on fire, although no-one knew who he was.
  

Your is a possessive determiner to mean belonging to or associated with the person or people that the speaker is addressing:

• Is that your car? I thought you had a black one.

You’re is a contraction of you are:

• You’re so clever!
  

Their is a possessive determiner and there is an adverb. They can be confused because they are pronounced the same:

• This is their house.
  
• There it is! That’s our hotel. The one with a clock tower.

Modal verbs are never followed by to, except ought to:

• I must go now. [obligation]
• We should sell the company cars. [desirable]
• I will arrive at 11.
• We ought to order our food now.

This rule does not apply to those words or phrases which act like model verbs:

• We are able to come to the meeting.
• We can come to the meeting.

Ought to is formal and you can use must [obligation, duty or correctness] or should [desirable] instead:

• I ought to go now. [obligation]
• We ought to sell the company cars. [desirable]

When we talk about age, height, weight, size and colour, we also use be:

• I am hungry.
• I feel very tired.
  
• I feel a bit nervous about the presentation tomorrow.
  
• I’m afraid we don’t have enough money.
• She’s under twenty which is a little young.
• He’s mature for his age.