Generally, the names of specific things need to be capitalised. By specific, I mean that there is only one of or only one type of. For instance, the fast-food chain ‘McDonalds’ starts with a capital letter. This is because it is one specific type of fast-food outlet, even though there are lots and lots of them around the world.
Names of places, historical events, religions, races, brand names, public holidays, days of the week, and many other words are usually capitalised. There are some common words that people capitalise when they shouldn’t, however:
north, south, east, west
When we use these words as directions, then we don’t capitalise them. If you’re using them as a noun, however, you do capitalise them, like in this sentence:
In the war, the North and the South weren’t very friendly with each other.
The other common thing that people capitalise when they shouldn’t is a season name:
summer, autumn, winter, spring