How much to sell BTC on Coinbase?

Could you please provide me with some insight on how much to sell my BTC on Coinbase? I'm a bit overwhelmed with the current market fluctuations and I'm not quite sure when is the best time to cash out. I've been holding my coins for quite some time now, and I'm starting to feel the urge to convert them into fiat currency. However, I don't want to sell too early and miss out on potential gains, nor do I want to wait too long and risk losing value. Could you offer any advice or strategies on how to approach this decision? Thank you for your time and expertise in this matter.