Improving is for everyone, for beginners or advanced, no matter the area. In my case, Illustration and Vector Art is what i will be talking about.
On VectorTuts+ site you will find some of the best tutorials, interviews with the artists of the moment, free brushes and other resources to help with your projects.
If you are a fan of Photoshop, you are lucky, they also have PsdTuts+.
They have a Premium Version with a huge library of educational content, premium tutorials, courses, e-books and more.
Another great resource for tutorials is the blog of Chris Spooner, Spoon Graphics.
The third best resource is another great design blog founded by the brazilian designer Fabio Sasso, Abduzeedo.
Vector Diary has some nice tutorials as well.
With all the resources out there you just need the time to get started and create your own beautiful designs.
Practice makes perfect !