I originally wrote this guide for my CSGO-Team, since we had some problems with this topic and our IGL sometimes went mad because of this issue.
I am gonna use IGL as the Strat Caller here, since this guide should also be helpful for PUG-players - it doesn't mean you have to become the IGL yourself, most of the time there will be someone in your group taking this job, but if not - why don't you give it a try?

This is your free time, your buy time and the time to drop for teammates, here you are gonna discuss the strategy for the coming round, maybe depending on your spawns.
Also, if your are playing in a PUG or premade with less than a full team, greet your mates - it will assure them off you having a microphone and the ability to use it.

1. Buy time - Drop time
   
   • To all of you without buybinds[csgobuynds.com] - please get yourselves some. You need to focus on what is happening at the start of the round and not look into your buy menu. It's not a laughing matter if you buy an SMG when your mate could have dropped an AK. Even less so, if there are two M4s lying on the ground with your team already fully armed - think of your economy!
     
   • Listen to your IGLs calls!
     If he calls a force-buy, you buy armor and the best weapon for your money.
     If he calls a full eco, take a look at your money and get a pistol you are comfortable with or stay with you Glock/USP/p2000.
     If he calls a full-buy, get armor>AK/M4>Nades (buy incendiaries/molotovs, these things are round-changers).
     What this is about, is - listen to your IGL and do what he calls and not what you feel like doing. This is a team-based game, you can't win alone.
     
   • This is the time to speak up if you need a drop. Wait for a call from your IGL, he may determine someone to drop. Also, take a look at your own money before buying - if you have a ♥♥♥♥♥♥♥♥ of bucks, you might be asked to drop an AWP for someone and get an AK/M4 from him in return.
   
   
2. Strategy
   Listen to your IGL, what he tells you to do at the start of the round.
   
   • Going for the picks? - Ok, cover all routes and see if you can get an Entry.
     
   • You have a good spawn for a certain position, so your IGL tells you to rush there and prefire the corner - so take your knife out and run. The ideal would be if the player right behind him could throw a support-flash.
     
   • Rush? - Alright, you run all together to the designated site and suprise the enemy just getting there, maybe they were even late in the get-to and you are there earlier than them. Just don't wander out alone and be fast.
     
   • If the IGL calls another tactics, just do this one (2/3 split, etc.) and ask your mates for flashes/smokes beforehand.
   
   
3. Spawns
   Be mindful of your own spawn and the spawn of the whole team, sometimes you will know if the call for a rush is coming just from your spawns. Still wait for the call afterwards.
   
   
4. Summary
   At the start, just give a clear call on what you need - weapons/nades/support and then listen to what your IGL is saying and don't interrupt him, even if his tactics killed you the round before, he is trying to win the game.

1. Format
   To efficiently call, I recommend using a unified format, after all, the information is supposed to travel clear and fast to your IGL and the rest of the team.
   Weapons(especially AWP)/Numbers - where - what are they doing - what will you do
   Example: (Dust2) AWP A-spot, one pushing short, I'm flashing short.
   You do this loud, clear and only what you know, not what you think
   NEVER CALL WHAT YOU DON'T KNOW
   
   
2. When and What
   Actually, you call everything you do and everything your enemy does.
   Which doenst mean you have to comment your every step...
   
   • Got eyes on the enemy? - the format is clear now, but it's important to make accurate calls - "All rushing long!" - now was it really 'all' or only 'four'? This can save your teammates lives as they will watch out for a lurk!
     
   • Plant the bomb - you should do this asap anyway but! - it depends on the situation where to plant. Do you need the money? - plant default. Is the site clear and you control every corner? - plant open. The important thing is to tell this to your team so that they can position themselves apopritatly.
     
   • Nades - you throw a flash? Where, when? Throwing a smoke? Where to? - you don't need double-smokes or teamflashes.
     
   • Rotation - either call for a rotation or say, that you are rotating yourself. Don't be too hasty and tell your team if you don't take the shortest route, for example, if you are going over T-Spawn or the like.
     
   • Steps - when you hear steps, tell your team if it was a single one or more than that and the suspected direction.
     
   • Kills - if you kill an enemy make a call and say if you saw more than the one you sent to the next life.
     
   • Deaths - look below.
     
   • Looting - this is about upgrading your weapons, did you drop an M4/AK on your death and your teammate only got an MP7 - tell him where it was. An especially good time to do so is when your team is defusing the bomb and the enemy is dead or saving.
     Think about the worth of the weapons - also chose an AWP over an M4/AK, but keep in mind that you probably won't need three AWPs. Also don't about forget nades, defusekits and pistols.

Got rekt? - ♥♥♥♥ happens. Tell your team where the enemy killed you from and where he is going (keep in mind, this could be a fake) and if you saw others. After that - keep it shut, let the players alive do their thing.
The only one allowed to making calls after death is the IGL, that is if your plan needs changing.
Now you have the time what you did wrong. Maybe it was an unlucky headshot you got there but maybe you didn't listen to a call or rushed through the smoke like a silver? Think about your own mistakes first...

If you read this far - thank you.
I hope this guide will help you in future games and maybe make the community a better one, I would be grateful for a 'thumbs up', if you didn't like it, you can give me a 'thumbs down' but I would be glad to hear your opinion on what you didn't like.
Also, tell me in the comments if you would be interested in a german version of this guide.

http://steamproxy.net/sharedfiles/filedetails/?id=180295347
(Funny thing is - I found this awesome video by WarOwl right after I wrote this guide)