One of the most important lesson I've learned since I got involved with cryptocurrencies on November 2017 is that to always buy when the market crashes & not when the market is doing good. This requires a lot of patience, it can be at any moment, sometimes just within 24 hours, 2 weeks or even longer before making any moves. It all depends on how low the market crashes & when it crashes. I bookmark coins that I want, keep an eye on those coin & check for the price in satoshis & as well as in USD everyday. It's best to have fiat waiting on Coinbase, GDAX or on other fiat gateway exchange platforms to get in on time to buy within the price range I'm looking to purchase at. Even though storing fiat/crypto in any exchange is very risky, as of right now I have no choice but to have them ready to go because for me it takes from 1 hour to 24 hours on weekdays to transfer fiat to GDAX & this service is not available on weekends but is completely free. I could also directly buy coins through Coinbase but I don't want to pay any fees. I use GDAX because there are no fees when trading with limit order, no fees when withdrawing crypto, $0.18 fee when cashing out any crypto amount to fiat & it's fast & easy compared to other options out there.
09/03/2018 BTC/USD - https://bitcoinwisdom.com/markets/bitstamp/btcusd
When I'm looking to buy a coin I check the all time high/low in satoshis & USD, I try to use that to help me decide how much I should spend per coin. Of course, even when I buy a coin at it's lowest, the price can still go lower but at least it's better than me buying when a coin is doing good or when the price is moving sideways. The reason I don't keep BTC, ETH or other altcoins waiting to be spent is because the value is always moving up & down so I don't want to be caught up with loss value on those crypto that was waiting to be spent, unless I have no fiat & want spend my holdings. Alternatively, I could also turn my fiat & crypto to USDT (Tether) because USDT barely fluctuates so the value always stays the same at almost all times.
So to conclude, when I'm ready to buy a coin, I buy BTC or altcoin with fiat depending on the paired coin & then BTC or altcoin to the coin I'm looking to buy. Obviously, everybody does that but not everybody keeps fiat ready to be spent when the market is down. I do this because I don't want to miss out on very low SALE prices on coins that I've got my eyes on. The lower the price you buy a coin at, the higher the profit in future when the price goes back up.
Thank you for taking your time to read this post, I hope this brings some type of value in your crypto journey. If you have any comments, questions please let me know.