Use small buy-ins, and don’t margin trade or short unless you know your stuff. The smaller your bet is compared to your total investable funds, the less risk you are taking on every bet (one of many insanely important things we are covering here). Putting it all on black is tempting, but then if it comes up red, you have nothing left to invest. Live to fight another day by learning to manage your buy-in size. As a rule of thumb invest 1% or less per buy-in (yes, that small, really; losing 100% of 1% leaves you with 99%, losing 1% of 100% leaves you with 99%. Small bids offer the same bet, but with way less risk). Put reward aside and practice risk management and capital preservation until you are very experienced (and thus, by logical extension: don’t margin trade or short unless you know what you are doing, as those leveraged bets magnify your risk by their very nature). See Kelly criterion.
There are a number of tools you can use to maximize profits and minimize risks, such as margin trading, leverage, and stop-loss orders. Shorting Bitcoin and other cryptocurrencies can be done in a variety of ways. Just looking at the Bitcoin price chart for early 2018, you can see that those that spotted the downward trend in mid January and made a short trade would have made 40% profits by exiting one month later.
Consider Diversifying. With the above advice in mind, there is nothing worse than getting frustrated with BTC, moving to ETH / alts and missing a BTC price spike, then moving back into BTC and missing the ETH spike. This is very easy to do given the rotation, and the natural urge to “FOMO buy.” If you have some of your funds in all the coins you trade, you’ll avoid missing out on a unicorn (a term one can use to describe an odd event, like a giant price spike in a short amount of time). If you diversify, especially when prices are low across the board, you’ll avoid some of the urge to jump into one coin mid or late into a run and out of a coin just before it goes on its run. In other words, although it isn’t the most profitable tactic, diversifying is good for one’s sanity in a number of important ways.

Figure out if you want to go long or short. Are you going short with every penny you have to invest, or are you going to go long with some and short with some? Long-term investors will pay a lower tax rate if they can hold for over 12 months, but as a trade-off, they WILL have to sit through corrections (likely seeing their balance go down 50% plus on paper as often as they see it go up). Short-term investors can avoid corrections if they are nimble, but they’ll owe taxes on the profits from each trade they do along the way (see: how taxes work with cryptocurrency to understand how the long term and short term capital gains tax work with cryptocurrency).
Don’t be greedy. No one ever lost money taking a profit. As a coin begins to grow, the greed inside us grows along with it. If a coin increases by 30%, why not consider taking profit? Even if goals are set to 40% or 50%, you should at least pull out some of the profit on the way up in case a coin doesn’t reach the goal. If you wait too long or try to get out at a higher point, you risk losing profit you already earned or even turning that profit into a loss. Get into the habit of taking profits and scouting for re-entry if you want to continue reaping potential profits.