The two links in my signature are the main ones.
With CCleaner, run the cleaner and the registry cleaner. It's also good to uninstall any unwanted/unused programs before you do that. Make sure read through all the options in the cleaner, so you don't delete anything you want to keep.
Then, run Defraggler. It's a defragmenter, which I prefer to the in-built Windows one (better features, and I think it's faster too).
CCleaner also allows you to edit what programs and such start when you boot up the machine (this can also be done by going to Run -> msconfig).
On my netbook, I use mostly Google Chrome, and Firefox for stuff that doesn't work in Chrome (YouTube fails for me generally in Chrome, across all machines).
Finally, download+install both 'Spybot Search & Destroy' and 'MalwareBytes Anti-Malware' (the free one), and run through both of them.
What anti-virus do you use? I don't use one on my netbook, but I can't really recommend that to the average joe.
Do you have Windows 7? If so, you can disable unused services such as the Bluetooth driver, for example (unless you actually use Bluetooth with your netbook). I'm not entirely sure if disabling stuff like that actually gives you any more performance, but I've never found it to hurt.
Any questions or specifics you're after, just yell