Get a bad internet connection with bad hits for a few months!
Set m_yaw and m_pitch to 0.001 in your config. This increases the number of "grid points" on your screen your crosshair can "snap" to. Doing this will make your sensitivity seem waaaay low. After changing these two settings, I had to set my sensitivity to 45. Not 4.5, fourty-five. The menu slider doesn't go up that far so you'll have to drop down the terminal and use /sensitivity XX.
I played with a sensitivity of 45 for a month then switched to 90. The twitchiness was insane on my high-DPI laser mouse but it gave me precise control - just not so well at high sensitivity. It was basically training for when I dropped to the more reasonable sensitivity of 45. Playing with a high DPI meant I got owned a lot because I'd miss slightly where others did not, but keep at it. When you drop to a lower sensitivity again, you'll be able to snap right to your target hopefully.
Try setting your autos to semi-auto. I know it's not very useful when you get jumped up close, but it'll help you control your firerate for medium to longrange firefights. You'll be able to beat average G36-ers in no time. (obviously those that know how to tap their shots and make it count with the G36 will be more troublesome, so don't expect to pwn everyone)
Clean up your screen. I have the most basic playerlist - just the number of enemy and friendly players alive, because you should be concentrating on killing the enemy and staying alive, not on how high or low your score is. Yes, I do sometimes hit tab to see what my score is throughout the game but I try not to. Coming first doesn't mean you're the best - work on your ratio, not your kills. Getting 50 kills might place you first but it's pointless if you died 40 times. Also, turn off the netgraph and FPS counter - you don't need them to kill. (unless you're diagnosing network issues)
Try a different crosshair - I personally use the smallest dot in either green or white. Look at your crosshair, not your enemy; a small crosshair will make you concentrate harder on it as it's less visible.
Switch off gun visibility - it's just another distraction, especially with muzzle flash. It's stopped me stepping on a few nades sneakily thrown in from the side before, because I can see everything.
If you haven't already, set FOV to 110. I've watched from spec mode enough people get owned because they're using FOV 90 and I can see their enemy off to the side but they can't.
You could also practice your headshots with the Beretta, although this is best done with a small dot crosshair in my opinion. Once you can keep up with everyone else who's using an auto, switch back to your auto of choice and tap your shots like before. As for tapping shots, I'd say the AK is a good choice for practice, as the accuracy is lower and the recoil higher than that of the other autos. Those who can be as accurate with an AK as those with other autos will win, because their gun does more damage. It's tough, and I'm not very good at it, but it's worth a try.
Switch up your weapons a bit, try something you wouldn't usually choose. The UMP45 for example, is the most accurate auto, with same damage as the LR and M4 but pays for its' accuracy through a low fire rate. If you can handle it, it's great for headshot practice; not so great if you get jumped. Some people like the MP5K+silencer+laser combo - low damage but very accurate and very fast fire rate. You won't get so many kills per clip but you'll hear the hitsounds plenty! (Turn hit sounds on if you haven't already - it's a great indication of how much damage you've done to the enemy without having to look at the screen output) The downside of that is you have only one equipment slot left.
All guns feel different to all players. Personally, I can't use an LR with a silencer as I can't count my shots very well, but conversely I prefer the M4 with a silencer as the sound distracts me and again, I don't count my shots.
As a side note, try Quake's recommended scrim loadout - primary, sidearm, kevlar, helmet and your choice of laser/silencer. If you're playing TS you don't need a huge amount of ammo, if you're in a busy server there's ammo all over the floor. I only ever carry a secondary as a sniper now. Also, if you run out of ammo for your primary and spot a different primary on the floor, dump yours and grab it - you should learn how to use all the guns to become a more rounded player. It might keep you alive longer too.
Another optional choice is to reduce the quality of the textures. I find that the lower quality textures end up looking like smooth patches of colour, and find it easier to spot enemies against such a backdrop. It might not work for you and you might prefer the better graphical jazz, but for me I consider it less visual information to process.