1. First of all... know thy enemy. If you for some reason didn't know this handy command "hud_combattext 1" will allow you to see damage numbers next to enemy models. Some HUDs can probably overwrite this see here[playstuff.net] and here for more details. Review what each class max hp and max buff hp (x1.5) is. Heavy can probably survive 400 and still hurt you. Too much stuff to remember... just assume the following:
   
   scout/sniper/spy/medic 125-150 (need 2 directs)
   pyro/demo/solly 175-250 (need 3 directs, pyro... well... adjust for reflects awesomeness...)
   heavy 400 (need 4-5 directs)
   Math is hard.
   
   *pipe* *direct* *meatshot* (pipe, rocket or shotgun that deals about 100 damage each)
   *headshot* (150 obviously, with charged hs a good sniper should take out the target so doh...)
   If it's anything else DON'T BOTHER to call it.
   If you did two pipes 75+70=145 just call *<class> took pipe* since it's not enough to call two pipes.
   
   Saying *someone is low* or *someone got rekt* is misleading most of the time
   
   
2. Things EVERYONE call AT ALL TIMES
   *combo <position>* (if you see combo at new position, then call asap! especially if we have 100% uber)
   *uber call/pop <position>* ("call" is for Medic saying voice command when uber is ready)
   *sniper <position>* (only call when sniper is in scope mode)
   *med down/drop* (followed by cheers and cold champaign)
   *taking teleport* (if you call it a second earlier that Engineer might just remember that teleport is unsafe and he forgot to call it)
   *spy on <class>* if the spy is behind someone, or *spy as <class>*
   
   
3. Realise that your comms will have a roundtrip of about 0.5s due to network latency and another 0.5-1s due to people reaction. Also Medic Uber pop has around 0.5 delay from the moment you press the magic button. So don't rage when people didn't call spy in time for you to react or your Medic didn't pop in time to save you from surprise Kritz.
   
   
4. Always agree how to call locations before the game (usually during map talk you do that anyway). Don't just assume that everyone know "China" or "Shack" to be the same. You can check this wiki[comp.tf] for naming convention. You should try to call absolute positions and not relative to you.
   
   
5. Sniper calls - *sniper <position> / down* (it's the only thing expected from a sniper - easy to play :D)
   
   
6. Spy calls - all things from point 2 and ideally after every "med down" check their medigun in 15sec (they do that in Div 3). Spy is usually the eyes of your team. Most times good comms from spy mean world more than tricky backstabs.
   
   
7. Medic calls - Uber percentage at 25, 50, 75, 90, 100%, and in case of your unfortunate death always say so. When you spawn say so someone can pick you up. If you have some free cranium capacity left try to track enemy Uber percentages since you have your meter to measure against (they do that in Div 3 again).
   
   
8. Don't interrupt who ever is speaking at that moment for your regular comms (unless you are calling Uber pop, Spy or Godzilla!). Queue your info up. Don't repeat what the previous man said. Keep your comms short! Call ONE most important thing, don't call everything at once. Ideally you should be giving out one piece of HELPFUL info per 15 sec, your call should be about 1-1.5s long!
   
   
9. In case you forgot location names use directional calls relative to your combo (or Medic) e.g. "Pyro close left". Use approximate directons easy to understand, don't try to be Google Maps. (Special thanks to Quintosh for this one!)

1. In lower Divs you can probably do pretty well without main caller. Demo telling Medic when to Kritz is not it. Main caller is someone from the team most experienced who can do shooting as well as thinking at the same time.
   
   
2. Also main caller should have some weight (pun intended) and have the whole team support what he does. Demo and Heavy usually do best main calling because they are the combo. Medic will do fine in lower divs or if he did play a lot as either Demo or Heavy before.
   
   
3. A team has ONE main-caller, hence the name. No backseat maincalling should be allowed. However as you climb Divs counter-calls might work sometimes, just due to essential information you might be lacking at the moment. But it requires immense amount of practice between the calling partners.
   
   
4. Main calling is a bit of everything. If the team is good then main caller will only designate general directions. But sometimes you will need to tell specific classes what to do (this is usually maps with multiple entry points like Steel or Gravelpit). The timings are always crucial, because you have to finish talking and allow people time to react (see point 3 in Team Calls).
   
   
5. If something is going bad, try to rethink your approach. Raging is not an option. If anything no caller is better than bad caller.
   
   
6. Now when pushing ideally you should be doing damage to sentry>demo>heavy>med>etc in that order. If there are multiple targets in range main-caller should designate a target "FOCUS <class>" and EVERYONE around should deal damage to that one first.
   
   
7. Nobody interrupts the main-caller and if the main-caller interrupts then that person should queue their calls. Whatever main-caller said everyone should do without second thoughts (see counter calls). If main-caller said "push" then it means "PUSH NOW!" and your only valid excuse for not doing that is if you are in an engagement, or you are designated to hold last point.

Telepathic Ryuu: another valid reason
Telepathic Ryuu: is you are dead
Telepathic Ryuu: :D
Kengur: no, that's not a valid reason :P