If you want to start trading, place your trades either via a demo app or, even better, with a piece of paper and pencil. This will give you a very good feel for how well you can rely on your own instincts and how you react in "tricky" situations.
After you have practiced this for 1-2 months, you can start betting real money (or BTC). However, only very small amounts at the beginning, preferably in the single-digit dollar range. Only after some time (and many lost dollars) will you have gained enough experience to actually enter into larger trades.
So there is actually a second rule to add to my golden rule: take your time practicing!