Hello,
I have posted an in detail guide "How to Optimize Dota 2 and PC for best gaming experience" at my site Dota International.
You can read the guide on above link, but here are some summarized points of this guide.
1. Optimize your PC for Smooth gaming:
You need to get some space free in your Hard drive, you can do it by deleting Dota 2 Crash dump files, disk clean up and de-fragmenting Hard disk.
Next you need to shut down all heavy programs before playing Dota 2 so it does not consumes your PC resources. Pause all downloads so your bandwidth does not get eaten and you don't face lags etc.
2. Optimize Dota 2 for Smooth gaming:
Optimizing video settings, using console to customize your experience and other small tweaks and tips can help your in-game playing experience.
Remember its not a cheat sheet, its a compilation of tips, tricks and tweaks that will improve your gaming experience. I am really very sorry that I can not rewrite whole article here, that is why just gave a teaser glimpse.
In case you need to ask anything, feel free to ask.