How to Pubstar: Rushing – The Basics
Go speed racer, go!
You want to get in the enemy's nest as quickly as possible, catch as many off guard as you can, and put them through the meat grinder. You'll die every once in awhile, but the more you practice and use the tips available here, the more you'll instead look like a hero (or a hacker, depending on the server) when you pull it off; so I'm going to help you get there!
Firstly, you don't want to waste time buying each round, especially if the server is running a zero second freezetime (the time you get at the start of the round to buy your equipment). F2 (default key) is your rebuy key and friend, but it needs a little tweaking to be fully effective. Rebuy will not rebuy armor, or defuse kits! So, to save yourself valuable seconds, rebind your F2 (or whatever key you prefer if you're picky) with the following console command. If necessary, add the line to your autoexec config.
bind F2 "rebuy;buy vesthelm;buy defuser"
On your mark, get set...
As the round is about to start, hold down your forward key and tap your rebuy key. The moment the round starts you will already be charging forward (or will have to wait the few seconds of freezetime) and will grab your gear without needing to open any menus. Normally, you will be the first person on the move and will be able to get yourself into position to pick off or surprise the enemies as they approach. You may however, need to slalom between your teammates as most people will still be cycling through the buy menu rebuying their gear manually, but fortunately so will most of the enemy team. If there is freezetime, use it to get your M4 silencer on (if you so prefer).
Once you're moving, pull out your knife (or scout) right away for optimal running speed. Know the map! After enough plays you should have a good idea of where you can get to before any enemies show up. You will often be able to pull out your main weapon just as the enemy is coming into view, and has no time to react to your presence, *bang*, they're dead. I suggest tapping your pistol before your main weapon key, in case you need to do a quick weapon switch during the fight (there may very well end up being a lot more enemies than you were expecting, and it would be awful to suddenly pull out your knife instead of your sidearm).
Like shooting fish in a barrel
The last thing we'll go over today, is locations. Generally, your starting spawn point will decide where you will be rushing. My preferred map is cs_office, so it'll make a fine example. If you start right by the main hall, your best bet will be to rush front stairs or garage/back yard. If you start near but not right next to the main hall, your best bet will be to rush garage/back yard. If you start nearer the back hall, your best bet will be to rush the front office. If you start in projector room or in the middle of the spawn, well, you're not going to get a successful rush in so I suggest not trying to, as most likely you will end up getting counter-rushed or sniped before you even get close; but you can move around with your team and play a normal round, and this will also help trick the enemy so they can't predict too easily where you will be appearing next.
Practice getting these basics down, and later we'll go over more advanced techniques that'll help you thwomp the competition and become a pubstar.