How to make less laggy?

[Fire]

My pc specs aren't the best, but all my settings are on the lowest, I don't have really bad lag, but quite low FPS. Any help?

[Enigmantic]

I use Gamebooster to increase fps while playing some of my games and it works. Maybe you want to check into it if you are having fps problems.

http://www.iobit.com/gamebooster.html

[Hydra_360ci]

put
-lv
in the starup launch option.
https://support.steampowered.com/kb_article.php?ref=1040-JWMT-2947
BTW: stands for low violence. Guess what it does.

[DrizDro]

Just a setting check. If it's the lowest, the resolution should be Normal (4:3) and 480p. Use GameBooster, as recommended above. You should be fine, unless you have an ancient computer; L4D2 is really optimized for most PCs.