Agatha Christie, the acclaimed Queen of the murder story had very little characterisation in most of her novels. She only gave details where it would advance the plot. In todays crime fiction market though, characterisation must be a key part of your work.

We need to make our readers believe and empathise with our characters.

Firstly we need to look at what makes our characters real or just mere puppets we have put on the stage of our novel.

Consider the following.

'Michael is six feet tall with brown hair and blue eyes.'

That is from my notes about a guy called Michael that i'm thinking of introducing to my long suffering readers. It tells you nothing above the facts. Many begining writers would write something like this:

'The door opened and in strode Michael. He was six feet tall. His brown hair fell over his face, nearly hiding his steely blue eyes.'

I hope you're cringing as much as I was when I just wrote it.

It's awful.

Yes, it says what you want to say in a few sentences but you have a problem. It is all physical description. Plus that terrible cliche. Steely blue eyes.
There is nowhere for this description to go either. Even worse would be the following line added to the description.

'His green check shirt and brown trousers were mud stained.'

Now unless the green check shirt and brown trousers are a crucial part of the plot then the description is going to get a little tiresome.

Hey the guy wears shoes too.

'His brand new size ten brown boots were also covered in mud.'

Problems here too. For a start, Any US readers who are not familiar with the UK system of shoe sizing will be confused. That is a no-no. If you confuse the reader then they will stop reading. The first person of note who will read your submission if you send it to a publisher or an agent will be someone who's overworked, overstretched with manuscripts and looking forward to bedtime. If they get confused, your manuscript will only end up in 1 place.
The reject pile.

Well that's what not to do. Let's see if we can improve matters a little bit.

By the way. All that information I have just written will be useful for our character. We'll use it.

Get a small notebook for characters. 1 character per page.

Michael.

Height 6 feet
Hair brown.
Eyes blue
Green Check shirt (Does he hve any fashion sense?)
Brown trousers (pants)
Brown shoes ( size 10 ) Check US equiv.
Clothing covered in mud.

Let's do it.

Unless your character Michael suffers from total amnesia, he must have a past that he knows about. He must have 2 parents. Four grandparents and so on.

Let's start with his parents.

The first things I want to know about Michael's parents are.

Does Micheal know who they are?
(If not, was he raised by the State? Adopted?

Does he know only 1 parent? Was he raised by his Mother/father as a single parent?

If Michael knows one or both parents then are they alive or dead? If alive are they still living together. Is one of them in a nursing home? Are they divorced? Has one parent died? Has the other re-married? What doess michael think if this is the case?

Answer these questions and we will get to know Michael a little bit more.

Again, we will summarize the answers to these questions. The answers are part of what makes Michael unique. For instance, if Michael had been raised by his maternal grandparents on a farm in the country, he would be a different person than if he had been raised by his single parent mum on an inner city housing estate after his drunken father walked out on the family when he was a baby.