size of the sprites

that size should sprites player

If my project is for a screen resolution 1024 x 600.

   

that size should sprites player

If my project is for a screen resolution 1024 x 600.

for platform game.

I'm not sure what you mean. Can you try explaining what you need in more detail? See Tips for posting in the 'How do I?' forum.

This is more a matter of composition than anything else.

So the answer is: it depends.

Draw a mockup level and deduce the size of your character from it. Keep in mind that you might adjust it after some playtest though. So wait before creating the final artwork.