Early career players tend to play too many hands, that is, if not all of them. They don't understand the math of the game, the importance of proper pre-flop hand selection, nor are they concerned with being dominated. Some do so because of the adrenaline that the game provides, but they are bound to fail in poker.
Poker is an extremely technical, tactical and intellectual game. If you don't mind losing money, ok, carry on playing all, or almost all, hands. However, if you feel that your competitive spirit has been speaking louder, wanting to make you stop being one of the players who finances the sport, I suggest that you immediately start making a reasonable selection of pre-flop hands and play a number much lower of hands in your sessions.
Another clear mistake in beginning players is their passivity, both pre and post flop. Although they play a lot of hands, they do it extremely passively, limping and calling when the correct play would be raise.
Still, they usually go to the river to hit miserable games that, even when hit, is not enough to win the hand. They tend to play almost all aces similarly, as if the kicker doesn't make much difference. They call almost always on the flop and turn, even when they miss the whole board and, having anything, pay generous value bets on the river.
When they have great games, they play too slow with their hands too, failing to extract a lot of money in the long run.
They want to play, and they do it from the position they are in, with whatever hands they have, against any opponent. They don't understand the mechanics of the game and that money follows the clockwise flow on the table. Often, because they are out of position, they find themselves in delicate situations and don't know how to act.