Install a Firewall to protect your computer from unwanted inbound traffic
Firewall protects your computer from hacking attempts. Windows xp, vista and windows 7 has inbuilt firewall and you should enable it inorder to protect your computer from hacking attempts. You can use zonealarm free firewall which is more effective for any windows computer.
Installing windows updates frequently and enabling automatic updates is highly recommended which protects you from most of the vulnerablities. You can change the settings of updates from control panel.
Deleting Temp Files
Deleting temporary files and internet downloads will free up your disk space and it will make your computer run faster but you don't see too much improvements but still it is recommended. You can use Speedy PC to automate this task.
Optimizing registry keys
Optimizing your computer's registry is one of the most important task you should do when comes to computer maintanence. This can be done either manually or using automatic registry cleanup tools. Deleting invalid registry keys and orphaned registry keys will be a tough task for beginners so you may use a tool like Speedy PC to do this job.
Using Antivirus software
Using antivirus software on any windows computer is always considered mandatory if you don't want to get your system infected with virus or any malicious programs. You can use free antivirus or paid versions but has its own pros and cons and it is up to the user's preference.
Defrag your computer atleast montly once using the system tools available within windows. You can schedule defra computer at your convenience. Your computer hard disk may contain fragments due to deleting files and copying new files and over a period of time the tiny fragments will start to rise and it will affect your computer performance so why not use defrag.
If you follow all the above steps you can tune up your computer easily.