What are the best ways to accumulate XP to get weekly rewards?

I bought CS2 Prime and I'm trying to level up to earn rewards. I only play in casual mode, so I only get 50/60 XP per match. The game also indicates that I have excess XP that will expire in 8 days. I bought Prime yesterday. I would like to know which game modes are the most rewarding for leveling up and obtaining rewards.