If you simply want to compile a new version of your currently installed kernel (for example, to enable SMP support), then the best way to proceed is to install your distribution's kernel source package. After doing so, you should find a bunch of new files in /usr/src/linux.

However, there may be times where you want to install a new kernel. Generally, the best approach is to simply install a new or updated version of your distribution's kernel source package. This package will contain kernel sources that have been patched and tweaked to run optimally on your Linux system.