I know the concepts of Constructive Crit, people give it out in different ways, it entirely depends on thier taste and the Graphic you have made.
Newb's can get better Various ways besides Comments on your Works.
Try Tutorial sites, such as goodtutorials.com, pixel2life. They can help you improve and generate Ideas.
Go on deviantart.com and look for Brushes and Textures, they help.
Graphics is all about Ideas, what you think is good and how to execute it. So why not look at other peoples works, and it may aspire you to create something which in the end maybe really good.
You will make something that people will like, as there are loads of people on here who have thier own diverse taste and personalities.
Paitence is a key in graphics, over time you will get a decent level. It may not be fantastic or brilliant, as that isn't always the case - but you will improve no matter how big/small it is. Just keep at it