When you buy/sell via an exchange, try to use limit orders (try not to use market orders). On some exchanges, like GDAX, limit orders have lower fees than market orders. On GDAX, limit orders are free as long as they don’t fill immediately. Meanwhile, market orders result in a .3% fee, which is better than the 1.4% that Coinbase charges but not as good as 0%, especially if you are day trading. If your exchange rewards you for using certain order types, aim to use them.
Always pay attention to Bitcoin. Most altcoins (every cryptocurrency except Bitcoin) are pegged more closely to Bitcoin than Asian currencies were to the USD during the Asian Financial Crisis. If Bitcoin price pump drastically, altcoins price can go down as people try to exit altcoins to ride the BTC profits; inversely, if Bitcoin prices dump drastically, altcoin prices can go down, too, as people exit altcoins to exchange back into fiat. The best times for altcoin growth appear when Bitcoin shows organic growth or decline, or remains stagnant in price.