Welcome to Cryptocurrency trading! If you want to get the best rates for cashing out BTC into USD, you should always sell at the top, meaning when BTC is worth more USD. You will need to have fundamental knowledge (News) and also some basic technical analysis (Charting) to know if BTC is going to run (go up) or down.
Put it simply, for fundamental news, Bad news about Cryptocurrency = BTC price goes down, Good news about Cryptocurrency = BTC price goes up
As for technicals, this would be more advanced as you can predict if BTC is gonna go up or down from indicators such as RSI (Oversold,Overbought), MACD crosses and price action. Check out https://www.babypips.com/
for more info.
We run a telegram channel that provides updates 24/7 on BTC price analysis, buy/sell signals and market intelligence.
You can check out: https://telegram.me/snipertradesignals
for more info and hopefully it will help you time cashing out your BTC to USD at a better rate.