I have only been trading since early December but these are the most important lessons I have learned so far. EDIT: A lot of salty salts in this thread. I never claimed to be an expert. These are tips I think would help newer people.
Don't give into FOMO - Identify FOMO by recognizing your emotions in reaction to a coin taking off without you. It's basically like Jedi being taught to become self-conscious and aware of dark side emotions rising within them so that they can better overcome it down the road.
NEVER buy at an ATH - Regardless of announcements, news, hype, partnerships, etc. If you missed out, just be patient. There is almost always a correction that will allow you a safer entry point, which segues nicely to my next point... EDIT: this is more applicable for coins that have seen a massive pump like x2+ gains. If a coin has seen steady growth and is at an ATH then by all means, have at it.
What goes up, must come down - If a coin moons, just like clockwork you can assume it will re-correct. It's sudden growth is usually unsustainable and a correction is most likely due whether that is within a few days, few weeks, or months, it is inevitable. We saw it with Ripple, XRB, NEO, and will most likely see it with VEN and WTC too.
Get a basic understanding of charts to become a value investor - being able to recognize that healthy corrections are usually in the range of a 40-50% pullback of the recent gains, this can help you find better entry points. The better price you buy in at, the more money you will make in the long-term. Buying in low also protects you financially and mentally against market dips.
If a coin is in the red, DONT PANIC - If you invested in a coin you believe in long-term, but it has dipped well below your entry point, do not view it with regret, see it as an opportunity to improve your position and buy more to reduce your dollar cost average. Think of it as the coin being on sale.
Don't be too stubborn/greedy to take profits - Contrary to this sub's obsession with the monolithic trading strategy of HODL. Sometimes the best move is to sell some and take some gains where they can be found (usually at an ATH), In the most recent market dip, this could have saved people a lot of money. Of course, in a bull market as seen in December, I would recommend just HODLing but in the last market dip, I was able to recognize early that the dip was not just a blip on the radar and was able to take profits on XRB, FUN, and SUB while they were still up and then get back in once they had fallen too with the rest of the crowd.
“Be Fearful When Others Are Greedy and Greedy When Others Are Fearful” - In a market as speculative as crypto, healthy skepticism can be an investor's best tool. This sub is one of the last places you will find healthy skepticism. When things were going as well as they did near the end of last month, there were a couple posts or comments that were heeding caution that the growth of the market was unsustainable (explained with good reasoning too) but it was just downvoted and ignored. It was like being at a big party and kicking out a person that was trying to tell everyone the music was a little too loud. Then the cops busted the party...
DYOR = DO YOUR OWN RESEARCH - Never believe any posts or comments saying a coin is "undervalued" or shill posts without explanations or well-thought-out evidence behind it. The majority of this subreddit has become a cesspool of people just trying to cheer their coin to the moon for their own financial gain. Unless they have provided you good evidence or reasoning behind their claim, assume everyone knows nothing. That's not to say that you can't learn things from this sub, many of the coins this sub shills have been right. But learn to look further into coins rather than placing blind faith into groupthink. Take an equal amount of energy to tear down a coin than you do with building up a coin. Look into the downsides and red-flags of a project rather than just searching for the great things about the project.
Never market order, ALWAYS LIMIT - Unless you are able to trade cryptos full-time (24/7), there is absolutely no reason that you should be trading with market orders. The market moves so fast and is so volatile that the present moment at your computer looking at one crypto is but a snapshot in time in a sea of a million more opportune moments. Set your limit orders and it will help you be much more disciplined in your entry and exit points and help separate your emotion from it. Use depth charts too to help position yourself in front of big buy/sell walls. EDIT: I'd like to add that a good strategy is to buy and sell in stages. This helps hedge your bets if you are uncertain how far a coin will dip vice versa how high a coin will go.
Don't invest it all at once, always have some liquid funds ready - When you first get into crypto, you will be tempted to use all your available funds to buy all the coins you like right away. Keep some ETH/BTC/ or LTC available on the side to allow you to be ready to pounce should there be a really good deal or a pullback on some of the coins you are in on. You should also keep some FIAT on Coinbase, GDAX, or Gemini to allow you to get a good deal on the big 3 should there be a dip, rather than panicking and trying to get your money transfer through to buy.
Hope this helps any newbies out there