So let me say first that at your rank, it's important you just focus on practicing.
The fact is there is no miracle-tactic or upgrade. It's just how you use what you know and what you have to your advantage.
Get a feel for what you prefer. Do you like rushing? Are you a defensive player? Do you prefer stealth?
Once you answer these questions for yourself, then you can start capitalizing on them.
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"Do not pray for an easy life, pray for the strength to endure a difficult one"