Clean The Registry
The Registry is where Windows stores information about your programs. Over time, this too can get cluttered and may affect performance.
You can use a Registry cleaning tool such as CCleaner to remove redundant program entries and the tool to tweak your system are available here to download.
Defragmenting Your Hard Drive
If your computer is like a car, then defragmenting is like the motor oil. You need to do this at least once a month, it is the one thing you should do every month.
Here is how defragmenting works: Your computer saves files to areas of the hard drive known as clusters. Ideally, a single file will occupy adjacent clusters, enabling your programs to retrieve that file quickly with minimal drive movement. But as you create new files your computer saves them near old ones, and when you modify old ones the new information gets written to more distant clusters, and over time a single file can get fragmented, or scattered over several nonadjacent clusters. Multiply this by the number of modified files on your system, and pretty soon opening and saving files can get pretty slow. Add in fragmented system files that Windows or applications use automatically, and everything else can get pretty slow, too.
So, defragmenting your files is pretty important, and that is what I always do to How To Make Your PC Faster. So to get these fragmented files in order again, you can use a defragmenting program by running the Disk Defragmenter provided by Windows.
To do this, just click on the "Start" icon at the bottom left of the computer screen and then click on "All Programs", "Accessories", "System Tools", and select "Disk Defragmenter".

Tip: The defragmenting process can take from a few minutes to several hours, so I recommend you to allocate a time where you would not use your computer for this purpose. I usually let it run overnight. And make sure that there are no other programs running in the background, this could slow down the defragmenting process.
If you have more than one hard drive, select the drive you want to defragment and click Defragment. If you have Windows 2000 or XP, don't bother clicking the Analyze button in the Disk Defragmenter dialog box; it may tell you that you do not need to defragment the drive, but if you have not done so within a month or more you should do it anyway.

In fact,
defragmenting once a month should be your goal; this is just often enough to prevent excessive fragmentation before it manifests itself in poor performance, and it prevents the defragmenting process from taking too long. Even if you are fastidious about defragmenting once a month, you should set aside an hour or so for the job.
Streamline The Windows Interface
Windows XP (and the new Windows Vista) has a number of effects that make working with files and folders on your screen more pleasing to the eye, such as smooth animated menus and transparent windows.
However, these use the processor too which means they can cause slowdown. Right-click the My Computer icon on the Desktop and click Properties. Click the Advanced tab and under Performance, click Settings and you can choose to switch off some of these effects.
Tweak The Page File
When Windows uses up all the available RAM memory in your computer, it turns to the hard disk for help and uses a Page File as extra space to work with. If the Paging File is too low, Windows can run slowly.
Right-click the My Computer icon on the Desktop and clickProperties. Click the Advanced tab and under Performance, clickSettings then Advanced and you can Change the Virtual Memory settings.
The System managed size option lets Windows determine the best settings for you, but you can choose to set your ownCustom Size if you wish. Type in the amount of disk space you want it to use.
There are varying opinions on what is the best setting, but many recommend putting it at 1.5 times your RAM - so for example if you have 512MB of RAM, you would set both the Initial and Maximum size boxes at 768MB. Click the Set button to accept your changes and see if performance has improved.
If you have plenty of RAM for your computer to use, then setting a large Page File is unnecessary and will just waste space on the hard disk. You should not disable the Page File completely though, as certain programs require it to run properly.
Update Drivers And Windows
In order to make your hardware work properly, Windows needs special programs called Drivers.
It is also important to ensure your Windows system files are up to date. This can help fix problems and protect against security threats.
Speed Up Games
Games performance, especially for demanding 3D games, is very dependent on hardware, specifically the graphics card and also your processor and RAM memory. If you want to run the latest games at their highest quality settings, you will need to have powerful hardware.
However, there are things you can do to help your current PC run games better. First, make sure you have the latest drivers for your graphics card by visiting www.nvidia.com for Nvidia GeForce cards or http://ati.amd.com for ATI cards.
Most PC games include display options in their menu screens. You can often choose from a simple performance setting - for example: Low, Medium or High, or you can get more involved with advanced options. Some games let you tweak or switch off things like shadows and other special effects that can put a strain on your system.
Often, it is a case of experimenting to get a good balance between visual quality and performance. A common setting to tweak is the resolution: choosing a higher resolution will mean clearer, more detailed screens but can cost performance. You can only go up to the highest resolution that your monitor can support.
When playing games, you should make sure not to run other programs in the background, especially anti-virus software, as these can contribute to slowing down your game.
Upgrade Hardware
Upgrading hardware such as RAM or the graphics card is a common way for PC users to improve the speed of their machine.
PCs bought from stores will often only have integrated graphics cards which are not powerful enough to run demanding applications such as the latest games. Many users later choose to replace these on-board cards with a better graphics card from the Nvidia GeForce or ATI Radeon ranges.
Sometimes you will not be able to get the most out of your brand new hardware without replacing other components which support it too, such as the PSU (power supply unit). You will also need to make sure any new hardware is compatible with your current PC's specifications before you buy it.
More advanced users can investigate the technique of "over-clocking" hardware to squeeze as much power and speed as possible from it, but this must be done with caution as it can cause physical damage to components.
Windows Vista users can take advantage of a new feature called ReadyBoost which enables you to plug in a USB memory stick which the computer can use as additional RAM memory.
The Windows Experience Index
A new feature for Windows Vista is the Windows Experience Index, which is aimed at helping users understand how well Vista and the software running on it will perform on a specific PC.
The PC is awarded a score based on its hardware configuration. When buying certain software, you will see a recommended Windows Experience Index score that a PC will need in order to run the program properly.
More Information
There are many sites on the Web with advice about improving performance and tweaking your PC. One of the best sites to check out, which has useful guides for tweaking your system settings and improving performance of specific games, can be found at www.tweakguides.com.
There are also many programs available which claim to be able to boost your PC's speed, however it is worth doing some research first as sometimes these programs can actually have a detrimental effect.
If you are looking at upgrading or buying new PC hardware, www.tomshardware.com has reviews and comparisons of PC components.