Throwing a grenade is an art: CS:GO

Grenades and tactics

 Grenades
Decoys are dumb. Decoys are only useful in such specific situations that you would be better off spending the money on a flash which ALWAYS has utility. The order of priority for grenades ALWAYS should be
1. Smoke
2. Flash
3. HE

Smoke over flash? ARE YOU MAD? No, and I'll tell you why. Flashes win encounters, but smokes win rounds. Controlling space is VERY important. It's so important I cannot properly articulate it. Always go for a smoke over a flash. Hell, when you're backed against the wall you can always fake flash with your smoke. It's more important to die for an awesome smoke and take a site than it is to flash and make a frag.

Also, defensive smokes are God's gift to CT side eco rounds.

If you want to get really tricky throw your nades while running backwards for extra floating. This way you can drop some awesome flash bangs.

What about Molotovs?

At our level, molotov grenades are priced out of our general tool kit. They require high level team play to be highly effective, as you can use them to zone out your opponents and push them into your team mates' loving embrace. For 800 bucks, you better not screw it up. For example, using molotovs at B on inferno you can zone players out of new box or oranges. I don't recommend using them unless you are playing with organized players who understand how to combine them with team play to secure sites.

If you're playing defense you'd be better off stopping a rush with a smoke, because armored attackers can run right through a molotov with only 20-30 hit points of damage. No one survives running through a smoke grenade. 

 Strategy and tactics
Get aggressive. The peeker in CS has an advantage. Peekers advantage means you’ll see the defender before he’ll see you. This is true in all situations except when peeking against an AWP already in position. Make people react to you. You never want to be reacting to others. By playing aggressively you get to dictate flow. Now, if someone knows where you are you need to readjust immediately or push them. Think of it like Judo, you need to use your opponent’s momentum against him. So let’s say I unpeek a corner, and you’re coming after me. I’m going to wait until the very moment you step in and begin to come around the corner, then, the very moment you’re moving to engage, I’m going to come out on you. By sweeping into someone’s turn I’ve now caught them flat footed and can finish them off. This is a very important lesson. Aggress into aggression.