Meh I might post a book anyway, but based on my knowlegde of the Core 2 series mainly.
There are plenty of little guides on the internet about OC. A good one is here
http://www.xbitlabs.com/articles/cpu/display/oc-guide.html . Just type overclocking guide into google and you will find heaps on the topic.
Before you start to do overclocking be sure to know where the clear CMOS 2 pins are on your motherboard. They will be 2 little pins that are next to the round battery on your motherboard. Basically while your experimenting with overclocking and you get to a point where your computer just will not boot you give a connection between the 2 pins and it resets everything back to default (call it an emergency measure lol, ive used it about 3 times). You can overclock the RAM and graphics card but they arnt as good overclockers and can make the system unstable easy.
A program to stress test your computer for instabilities is called Prime95 (people normally run that for about 6 hours after overclocking) and Coretemp to monitor temperature. The temperatures I reckon shouldn't go over 70 degrees C, however others believe it to be 60 degrees C (so 60-70 would be tops). The computer normally sounds an alarm at about 80 C and auto shutdowns at about 90 C, if it didnt it would probably starts to die around 100 C (called the t-junction if you sore it on CPUID)
Another note to make when you do start overclocking the CPU voltage, keep the limit to about 1.45V (that is if your CPU is similar to my Q6600 or Q9550, u might have to research what a safe value is). It can handle more, but best to keep it at or below 1.45V otherwise the processor would only last 6months or so. I got mine to 1.55V once which the CPU probably would of only lasted 2-3 months tops.
Most motherboards if you overclock the frequencies a little bit to much and it fails to boot then the computer will reset itself 3 times and revert back to default (but if u go to far over even the BIOS will fail to load that is where the 2 pin CMOS CLEAR comes in hehe).
Just read up a bit on that site and other sites that google "overclocking guide" spits out you will get an understanding and become more comfortable in doing it. Everyone starts somewhere, even I started with reading guides.
Other general notes: you can maybe overclock the RAM only about 100-150Mhz or so, over that I wouldnt really recommend it because they can become rather unstable. Graphics cards I wouldnt overclock at all because you can only overclock a little bit with gives basically a very small performance gain and they can get unstable easy. However there are programs for it and guides.
When you start OCing just increase the frequencies little by little (like 10mhz increments, keep the mulitplier the same at max (x9 normally)) then run prime95 for 10-30min if there is an error then increase the voltage a bit and try again until u reach 60-70 degrees or 1.45V, if still unstable then decrease the frequencies til stable. Be aware that most motherboards OC the RAM at the same time as the CPU, so use the RAM muitpliers to decrease the ram frequencies back to normal or little bit over. Instead of OC to the extreme u can OC for a reasonable stable value and leave it there (i can get mine to 4.1Ghz @ 1.55V since i got a good cooling system temperatures weren't a problem, but at those voltages the CPU was under serious strain and would of only lasted a limited time before it died). A reasonable value for mine is about 3.2-3.4GHz, but i went to 3.6GHz.
Well hope that all helps, just read up on it and you will get the hang of it.
Core i5/i7 follow a very similar process, but have an extra QPI that you can overclock. Personally I leave it, but you can overclock it slightly. Just like overclocking a normal FSB.
