The most annoying mistake is over-playing, I played with few bitcents and reached really good profit but kept going for more until I lost the deposited and profit money. I think over-trading in general is a big mistake that can even lower the possibility more than the house edge.
You should know your limit and don't do that usually because it will just make you piss when you will lose a lot of money. It's not over trading but it is over gambling, you are just not aware of what can happen when you will not stop on the right time. Also control yourself when you gamble, so that you will not be losing your deposited and profit money.