I have never done this before. Please let me know in the comments what I got wrong.
1. Windows 7 Laptop and use Firefox browser.
2. Socks5 proxy (911.re)
3. CCleaner
4. Buy credit card from brenumb
5. Card Gift Card
6. Exchange Gift Card for XMR (Local Monero)
7. Exchange XMR for BTC (Agora Desk)
8. Exchange BTC back to XMR (Local Monero)
9. Spend Monero on Darknet or Exchange for Cash (Local Monero)
For steps 6-9 I would use different accounts for each step and then never use them again. I would also use different wallets each time that I would never use again (Electrum and Feather Wallet)