First of all, you shouldn’t get desperate and pressurize yourself if you are not getting the frags. This will only worsen your gameplay. One should stay calm and only focus on staying alive in every round rather than risking and getting frags (and I’m not asking you to sit and camp at one place). Prioritize things – First, stay ALIVE and then, think about picking enemies and winning the round.
Then comes gaming sense and accuracy rather reaction speed. When holding – Know what can be the approach points of your enemies, and stay alert and focused. If you are holding a perfect position and you’ve got great weapon accuracy, you’ll pick your enemy(s) easily. Great reaction speed will only be a bonus here. When rushing – know where to flash and how to rush and spray. That’s it.
Know your weapons. Understand the spray pattern. Trust me, mastering spray is a single best thing in CS. You can even pick a magger at long distance if you are great at it (and I’m not talking about burst fires, but spray). Bonus tip – spray half round of bullets and do heavy damage, and then pull your deagle – do your magic (and then if still needed, switch back to rifle and use rest of the round of bullets – never fails).
Lastly, if playing on pubs, never blindly listen to the call of your mates. Play your smart game and win the round.
P.S. – These tips will not help you improve your game (only practise will) but, will definitely give you the necessary improvement boost.