About the tweaking, whenever you make a major change......
Disable mouse acceleration.
It is absolutely vital to disable all mouse acceleration when playing Counter-Strike. With acceleration on, you will not be able to play consistently. For example, you might move the mouse 6 inches to turn 180 degrees, then you move the mouse 6 inches another time, and depending on how fast you move the mouse you might turn 100 degrees, you might turn 270. This uncertainty in mouse response inevitably limits everyone's potential.
The easiest way to make sure any variable mouse sensitivity is disabled is to uninstall your mouse driver from the 'Add or Remove Programs' part of control panel, afterwards in mouse properties uncheck 'Enhance Pointer Precision'.
After doing this, some residual acceleration may remain, as Windows gives no way to completely eliminate all cursor acceleration from the control panel. This is where the CPL mousefix comes in. To use the CPL mousefix simply unzip the folder and click on the .reg file and say yes to anything that comes up. All it does is change two lines in your system registry to completely stop all mouse acceleration. Remember if you have used Mouse Acceleration for sometime, and have gotten used to it, this is one of the hardest settings changes to get used to. It is completely worth it to adapt to playing without acceleration, so stick with it and you will slowly notice the improvement.
You can remove it, BUT ONLY AFTER you have given it an honest effort for like a week, here: http://www.pisstakers.co.uk/download.php?view.12
Adjust Windows mouse properties.
When I see people list their mouse settings, many players are putting themselves at a big disadvantage. Windows has a slider for setting pointer speed, but that doesn't mean gamers should use it. The reason is that changing a setting here can in no way make up for the dpi (resolution in counts per inch) a mouse has or doesn't have. Increasing the pointer speed even one notch, will make your cursor skip pixels. Losing pixel accuracy is not worth it when sensitivity is adjustable in-game. Lowering the setting here, throws away dpi from the mouse forcing you to use a use a higher, less precise sensitivity in-game.
At the highest setting, the cursor goes two pixels for each count. If you open up MS Paint, use the pencil tool, swing the mouse around to make circle patterns and notice how terribly notchy the edges are. This is not normal aliasing if you have the wrong settings in mouse properties it will make easily visible notches, not jaggies, it will look like teeth from a saw blade or something else bad. This is not the same as the normal stair steps on the edges of non antialiased graphics.
On the other hand, if you reduce the pointer speed setting, even by one notch, you get two different mouse sensitivities and your cursor will move, slowly to the right, and faster to the left. This is probably even worse than raising it, so KEEP THIS ON DEFAULT!! The default setting is the 6th notch in the middle and it wont interpolate or filter your mouse inputs, so you get the dpi your mouse is advertised. This may take some getting used to but it's worth it, you need to live with it if you do not want your per pixel targeting or sane mouse response compromised.
You can clearly see the differences between these settings in my screenshots:
In-game console commands.
There are settings that can be adjusted from the console that you can't access or tune as finely in the game menu that may be useful.
sensitivity "3"
This changes your mouse sensitivity... pure preference obviously. The only tips I can suggest is don't put it over 13 on 640x480, 10 on 800x600, 8 on 1024x768, or 7 on 1280x1024, or 5 on 1600x1200 or you'll for sure lose single pixel accuracy. You want to avoid pixel skipping if at all possible.
m_filter "0"
Although the concept of smoothing mouse inputs over the last two frames sounds attractive, this is something you want to have set to 0. Basically by averaging your last two inputs you are watering down everything you do with the mouse. You know what to do better than the computer does. This adds a slight bit of mouse lag too. I would only recommend using this if you have a mouse that is crappy and jitters alot.
m_pitch ".022"
This determines how sensitive your mouse is on the vertical axis. When you look straight ahead the most you need to turn vertically is 90 degrees up or down, but the most you have to turn horizontally is 180 degrees left or right. This means you could potentially lower this setting and gain precision with aiming height and recoil control. Adjust in small amounts like +/- .005 and set to your preference.
m_yaw ".022"
This determines how sensitive the mouse is on the horizontal axis. If you want to adjust your sensitivity in only the horizontal direction change this in small amounts like +/- .005. Set to your preference.
zoom_sensitivity_ratio "1"
This changes the sensitivity in relation to normal when you use a scope. Raising this increases the sensitivity when scoped, decreasing this setting lowers the scoped sensitivity. Many people set this between 1 and 1.2. Set it to your preference.
Finding the PERFECT sensitivity.
I can describe an excellent way of getting very close to your ideal sensitivity in-game. Make your own server, put on a map like de_dust2.
Start by looking at a wall somewhere in the open and fire a 3-5 round burst into it. Now keep the bullet marks in your crosshairs and start strafing, aim fixed as best as you can on the bullet holes. The goal is to be so perfectly on target looking at your bullet marks that it's as if there is a poll hinged from them that's attached to your gun, and you just rotate and move as one around the marks.
You can strafe around your marks from different distances, including close range and farther away to get a good feel for the exercise. Also consider what spots you play on your maps and the distances you usually will encounter enemies from while playing when you decide how far back to be from your marks. It also helps to move your mouse smoothly and not drag your hand too much while doing this exercise. When you are finished practicing, write down the sens you were using on a sheet of paper and get a calculator. (or use the windows calculator if you don't mind to Alt+Tab)
Now in console, type sensitivity and double that value. Try the same experiment again with twice the sens. Once you quickly get used to the new speed, see if you are tracking the marks better or worse than before. Write this sensitivity down on the sheet. Now you are going to compare to one half the original value, the calculator will help you find this, you only need to bother with precision to the nearest .001 when you write your sens down. Quickly adjust to it and do the strafing experiment and aim the best you can. While you are trying to decide consider the following: if a mouse sensitivity is too high you may find trouble controlling the crosshair and it may bounce around your marks and jitter, conversely if it is too slow, you may find yourself sliding off your mousepad or falling behind the bullet holes while you strafe.
Now look at the sheet of paper. Cross out the worst highest or lowest sens remaining, leaving your best two sensitivities on the sheet. If you kept the higher sens, double it again and test at that new higher sens. If you kept the lower sens, divide it by two and test at that new lowest one. Write down the new sens and again eliminate the worst highest or lowest sens remaining. If you found that the new one was better, repeat this paragraph, crossing out the worst lowest or highest sens until you get a 'worse' for the new sens.
Now you have two sens on the sheet above one you are 'worse', below the other you are 'worse'. Your ideal sens should be between them. Average the two sens by adding them together and dividing by 2, round to the nearest thousandth when you get decimals. Write down the average but don't test it yet. Instead, carefully test the highest and lowest sens remaining and decide which is worse, cross it out, then repeat this paragraph with the new two remaining sens until you can't for the life of you tell which of the two sensitivities are worse. Then average those two that were indistinguishable, and you now have very closely pin pointed your mouse sens.
I tried this method from different starting sens and always come within .05 of the same value each time. In the process of writing this guide I did this whole process on three occasions, first time getting 1.181, then getting 1.200 and another time getting 1.155. That is pretty accurate but there is some normal variation but it's less than ±5%.
So why is it different each time? First off because you are feeling differently on different days, it may be worth it to test more than one time over a few different days and from various starting sens. After maybe 3-5 trials throughout a week's timespan, average the different final values you have determined and that will be your long term perfect sensitivity.
That way no matter how you are feeling, you will be the closest to what sensitivity would be perfect for you on any given day of the week. This also means you don't have to change your sensitivity very often and when you do change it slightly (less than ±5%) you stay in your optimum "range" of good sensitivities. This is important, finding just one value and sticking to it! The mind likes consistency, and if you are constantly making big adjustments more than 5% up or down to your sensitivity you can expect to play inconsistently and have slumps more often.
And finally, go for optical mice and not laser.
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