A good question to ask is what makes a character memorable from books that you've read. In Game of Thrones there are a huge number of characters so making a character stand out is a big achievement. Picking one -- Hound, he is memorable by the way he is treated by others and the name is a great reflection. So a nickname can make a character stand out, especially if it fits his personality. Joffrey is because he is such a loon, that you have to hate him. So making your character an extreme makes them stand out.

A good character author is Michael Sullivan. His two main characters are complete opposites: a thief and a loner versus an idealist. Immediately the two are tasked to work together and initially one tries to kill the other. Gradually, they gain respect for each other, so some form of conflict can make characters memorable.

Bernard Cornwell is great at creating memorable characters and his method is almost a formula; take someone outside their comfort zone. Sharp is an example and he is an officer from the ranks so everyone hates him. In Rebel one character is a Northerner who decides to fight for the South. Why, I can't remember - but you immediately have a character that instills sympathy.

Another method of creating a character is to think of someone you know or have met (and possibly disliked?) and to ask what traits made them memorable. We all know someone that has impacted on our lives in some way and you might be able to use that. I have but mainly for side characters. It helps when writing as you don't forget them easily that way and you stay in role when writing about that character.

My last thought is perhaps random. Not the thought but the method. Create a table of characteristics and roll a dice for each column. Listing the characteristics would be interesting, moody, indifferent, happy, arse-hole...

So;

1. Nickname

2. How others treat/respect your character

3. Put the character out of their comfort zone

4. Make them extreme in some way

5. Chose from a random list and see what you get

6. Think of characters in books (films) that are memorable and ask why

7. Relate to people that stand out for you in your real life and use those traits.