You need one guy to buy armor. He will be crucial for this strategy to work. No matter what happens, there's no way this player will let counter-terrorists push banana. In the beginning of the round, his job is to survive and create some space for the rest of the CSGO team.
The support player will buy a smoke grenade and two flashbangs and the rest of the team can buy whatever they prefer to use. These four guys will be the main squad. They will go through second mid up to mid. Once they're in position, the csgo skins sale support player will use this smoke and these flashes to prevent the defenders from pushing through the smoke screen. After the flashes he will join his sidekick in banana while the rest of the team rush through CT-spawn. Now your dumbstruck opponents on B will have to defend against attacks from both sides.
For this round you will need at least two smokes (if you buy more you can use them in mid to fake A or save them to buy more time after the bomb plant). Don't forget to pick up a few flashbangs. A molotov can be really useful to clear sandbags in banana. Either you're gonna toast the enemy hiding there or he's going to look down the barrels of your AK47s, say a quick prayer and embrace the afterlife.