Sentences start with capital letters. (This includes sentences within quotation marks.)
At that point, he turned and shouted, "She is in the taxi."
Even though it is within quotation marks, the word "She" starts a sentence. Therefore, it should be given a capital letter.
At that point, he turned and shouted, "she is in the taxi."
The points of the compass are only given capital letters when they form part of a name (e.g. South Shields).
I travel north at weekends.
The word "north" is simply a direction and does not form part of a name. Therefore, as it does not start the sentence, it is not written with a capital letter.
I travel North at weekends.
Do not capitalise a word just because it is an important word in the sentence.
Do not drink water from the taps in the gymnasium.
Although the word "water" is an important word in the sentence, there is no reason to capitalise it.
Do not drink Water from the taps in the gymnasium.
Use capital letters for the names of things or people (i.e. for proper nouns).
He sat at the top of Nelson's Column for 3 hours.
Nelson's Column is the name of a column in London; therefore, it is written with capital letters.
He sat at the top of Nelson's column for 3 hours.
Only capitalise the seasons when they have been given human traits (e.g. Winter's icy breath; the touch of Autumn).
The aliens will probably attack in the winter.
The word "winter" has not been given a human trait (i.e. personified); therefore, it is not written with a capital letter.
The aliens will probably attack in the Winter.
Only capitalise the principal words in titles.
The horse was eventually found in Ashton under Lyne.
The word "under" is a preposition and should not be capitalised. (Other words which are not considered principal words are "on", "in", "the", "a" and "an".)
The horse was eventually found in Ashton Under Lyne.
Consider carefully whether "however" should start a new sentence. (It nearly always does.)
The shark kept circling. However, we knew we were safe.
In its most common role, the word "However" is used at the start of a sentence to link the idea in its own sentence to the idea in the previous one. It should not be used to merge two sentences into one.
The shark kept circling, however, we knew we were safe. two sentences, not one
