Q.1 Why is it lagging?
Check latency, fps and rates. These are only three factors responsible for lag.
Q.2 Why my latency is high like over 100 or 200+?
There are only 4 possible reasons for this:
Playing on a server that is close to your location decreases latency or ping, lesser the latency more smoother and lag free the gameplay will be. eg. if someone playing from USA joins a server in Asia, then he would probably get over 100 ping because it takes some time for the packets to travel over such larger distances. So choose the location that is closer to you, you can see the list of servers location-based from here www.game-monitor.com
Make sure you are not downloading or uploading anything or some background process may be windows updates or some other process is utilizing your network resources, unless your bandwidth is very high. Because it hogs the bandwidth and make your game lag.
May be your ISP is having some routing problem, (not choosing the shortest path to the server).
Not playing the game on recommended internet speeds or lesser than that like dial-up connection leads to higher latencies. Playing on a wireless satellite or mobile connection sometimes may lead to spikes or sudden ping jumps.
Q.3 Why my fps is low like below 60. and they fluctuate alot?
Either the game is not running on recommended system specifications (i.e low power processor or graphics card or system RAM) or some other process is utilizing system resources. You can try freeware Game Booster from http://www.iobit.com/gamebooster.html.
Q.4 How to check in-game FPS?
For counter strike 1.6 / source / or any valve engine based game type net_graph 1 in console to see the FPS, rates and ping. For other games like unreal tournament type timedemo 1 in console. Or just download FRAPS software to benchmark and also display the FPS on the corner of the screen.
Q.5 I have a good graphics card but still fps is dropping. why?
Check your task manager or process explorer for some other process utilizing the CPU or system RAM, because not only the graphics power is required to run the game, but also CPU power and RAM have to be available.
Check if your graphics card or system is not heated much, for graphics card, temperature about 80 degrees celcius is not an issue, but for CPU 80 degrees celcius is very high, a good freeware for this to check is HWMonitor to see the thermal and power status of your system.
Contact your hardware manufacturer for heating issues, if your system needs some cooling solution, go for it, but for counter strike 1.6, overheating wont be an issue.
Get a better CPU, because counter strike requires higher CPU usage, when more models and bullet fire is there.
Minimum recommended passmark score to run cs 1.6 smoothly is 800 and above.
Check your CPU scores from http://www.cpubenchmark.net/
Q.6 My latency and fps are all perfect but still its lagging. Why?
May be your (client) rates are low or server rates are low.
Q.7 What server rates should I play on?
You cannot change the server rates unless you have the rcon password of the server. But you can change your client rates.
Q.8 What client rates should I play on?
Open console and type in the following
Q.9 I want to start a server with maximum rates what they should be?
Q. 10 Will my server lag if I start the server at maximum rates?
It depends upon number of players and your bandwidth. For information visit http://csfragzone.blogspot.com/2010/01/make-lag-free-server.html