I have already registered on Project Euler to work on my skills some, but I am open to more suggestions. :D
Project Euler is really not the best place to boost knowledge of any language. You use your math knowledge (which you will acquire from other places still) and your language of choice to solve rather difficult problems. If anything, Project Euler exposes the limitations of your intellect, and those of your chosen language.
So you want to improve your C++ skills? Stick around on this forum and help Beginners.
Project Euler is really not the best place to boost knowledge of any language. You use your math knowledge (which you will acquire from other places still) and your language of choice to solve rather difficult problems. If anything, Project Euler exposes the limitations of your intellect, and those of your chosen language.
There's only one way to get better. Practice. Think of something moderately difficult to write, and just go write it. Don't be scared to fail and make mistakes, that's a perfect way to learn.