Do not invest the money that you cannot afford to loose.
This is valid for any investment.
Do not put your all money into a single basket!
Diversify!
True
and
True
but thats only the half truth.
Diversifying too much doesn't make sense if you don't have much money. Choose only a few coins you belive in and invest at least so much in them, that you maybe can appreciate the winnings.
For example if you invest into a coin, that has the market cap of over 1 Million it will probably only grow a maximum of 10x in near future. So if you invest only 10 Bucks you can have 100 Bucks then. If you are really poor, this may make sense, but not if you are an average american. You have to invest at least 100 Bucks to be maybe glad with 1000 on a 10folding. Maybe you have to invest even more, depending on your bankroll.
On the other hand, if you invest into a coin, that has a market cap of 50k you may be glad with an investment of 10 or 20 Bucks already, because it can go way more than 10fold. It maybe can reach very fast a market cap of 5 million if its good (so 100x). Also you can loose less, if you don't go to much. Those coins in the lower positions can easily vanish completely and the money is gone...