How do I buy ERC20 tokens?

For those new to the world of cryptocurrency and finance, the process of purchasing ERC20 tokens may seem somewhat daunting. Could you please provide a step-by-step guide on how to buy ERC20 tokens? I'm particularly interested in knowing about the necessary preparations, selecting a reliable exchange or wallet, funding the account, navigating the trading platform, executing the purchase, and any safety measures I should take to ensure the security of my investment. Additionally, are there any common mistakes I should avoid? I'd greatly appreciate your guidance in navigating this complex yet exciting field.