5 checks that save marks.

About a minute each. Tick them off before you hand in: this is where many lost marks are found.

Check 1
Did you answer the question?
Your first paragraph should answer the title, not repeat the topic. Say what you think in one clear sentence.
Before
Nowadays, many people live in big cities, and local governments have to decide how to spend their money.
After
Cities should spend more on public transport than on parks, because it affects everyone, every day.
Check 2
Every part of the task covered?
If the task gives you points to include, write about each one. If it asks for an idea of your own, add one: a single clear sentence is enough.
Example
Finally, cheap public transport saves families money: a monthly pass costs far less than running a car.
Check 3
Is your opinion clear at both ends?
Say what you think in the introduction and again in the conclusion. Don't sit on the fence until the last line.
Before
Some think parks should come first, while others believe public transport is more important.
After
In my view, public transport should come first.
Check 4
Does each paragraph do one job?
One idea per paragraph, each with a reason or an example. Two ideas in one paragraph (health and clean air, say)? Split them, and give each its own reason.
Check 5
Verbs, articles and spelling checked?
Read it once just for slips. The usual three: verb forms, articles (Life is busy, not The life is busy) and spelling (received, not recieved).
Before
I look forward to see you.
After
I look forward to seeing you.