Firstly, you must make it your mission to use the AK74 all the time. Do not snipe, do not change sprayer, make that your only gun for at least a month.
Train everyday, practice shooting at a Window at close range, medium range, and far range. Practice fully automatic shooting, burst shooting (2-4 bullet bursts), and single firing. Practice all of these whilst standing up, and practice all of these whilst crouched.
I recommend burst firing almost all the time, 3-5 bullet bursts should do it and you should be killing people in your first burst or second.
The most important thing is you become familiar with your spray pattern and find the gamestyle that suits you most. The AK74 is more than capable of killing people fast from any range you just need to play smart and focus on improving your aim.
Do not k jump all the time and do not k jump whilst shooting. Either use the regular jump or just walk with your weapon if you must move and shoot.