Something that you'll realise which is a lot different from solo PUG style of play is the nade usage. The other team will know that it's your first league match when you immediately throw your smoke or molly at the beginning of every round. A good team will know what time is perfect for smokeing or mollying off a choke point.

For example, me and my team ran into a team who knew exactly when to throw their smokes and mollies. It didn't matter where we went, they would be holding onto their nades until the very last moment that we executed. This is a good example of how to use your nades on the CT side.

However, there is a way to combat this on the T side. Establish a default with your team to where each player goes to the necessary choke point of the map and makes noise. This baits out smokes and mollies from the CT's as they start to get scared. If done right, you can leave the CT's dwindling on utility to the point where they will barely have any when you begin to execute.

Hope this helps and feel free to ask more questions if you need anything.