Most of the newbie traders common mistake is the Risk and Money Management.
They just trade and trade at first, they really not into risk management, that's why before anything else before you put a sell/buy order on an exchange, PLAN first, do risk management such as identify the target, stop loss, and entry price, risk: reward ratio.
Most of the newbies are ignoring that's why they ended up quitting in just after short period of time.
And they start with a wrong expectation: get rich quick. Too many beginners think, they start trading today and they'll be rich by the end of the week. Trading is a steady process of winning and losing but winning more than losing. This is not a get quick rich business – if one thinks so, he'll better get a ticket in Vegas.
It's all up to consistency, responsibility, discipline, patience and knowledge. First goal should be to break even for some months, then maybe 1 or 2R per month and so on. And returning 2R per month means if risking 20$ per trade, the overall profit in that month is 40$. Sounds little right …
But think in the long run rather aiming for a 20R trade but closing it out at .7R out of fear and then losing 2R in the next trade as the beginner has moved the stop while hoping for the big winner, steadily profiting 2R per month are 24R in 12 months and 120R in 5 years → risking 20$ make 480$ per year or 2400$ in 5 years.
Sounds still little? But if one gets better and he's more consistent he might return some 6R or 7R per month in future. And with growing capital the position size increases as well meaning higher results.