Never got around to playing that mod, going to go download it there.
You are going to die. You are going to die a lot. It might not be as painful as Starcraft, but it is in a similar vein.
Always, ALWAYS squad up (default is 5/f5 through to 9/f9). This lets you see the health and position of all the members in your squad at all times.
Train yourself to look for the icon placed on teammates. This prevents TKs. On that note: teammates who aren't in your squad have smaller icon than those in your squad, enemies have no icon.
Stick with other players, and when you die, spec the players with higher scores, this will give you a better idea of the right routes to take on a map.
Learn the map flow, there are no damage indicators (main emphasis of the game is flanking your enemy) so you have to know where you are getting attacked from. Speccing players is normally the best way to do this.
In the beginning, Support is probably the most forgiving class. Even at Private rank he has access to some nice guns as well as having the most health of any of the classes. However, try out Assault or Recon as well (Recon is my personal favorite). Just try to pick something that fits your playstyle.
Finally, use your mic/listen to other players. Like I said, flanking is key in this game. One of the best talents you can have is being able to use the Ghost effectively. YouTube- ‪NeoTokyo - Capture the Ghost Mechanics & Gameplay - Half-Life 2 Mod‬‎
Oh and have fun, that too.