Good discipline man. Poker is a tough game man ! Discipline is probably the hardest thing to grasp. I've recently gotten a lot better myself, as people have said there was no way I was folding a hand like AJ preflop or a pocket pair but now that is a common move for me to make based on the action preflop. Technically I am not a losing poker player, as I have made more than I have put in, but I'm definitely nowhere near successful. Practice, practice, practice!
Things i specifically learned though?
Position is very very important regardless of how it may seem. A weak ace should almost never be played in early position IMO but in many situations is a great hand to get in late position (based on action before you go preflop of course)
If you're getting bad cards and its ruining your mood, get away from poker for a while. A few hours at least.. you need time to forget all that and come in fresh. Once again something that may not seem helpful but it absolutely is in the long run.
Top pair isn't a free ticket to the pot! Even with top kicker. Don't go crazy when your AQ sees a flop of Qh 8d 9h... good hand yes but many draws that can bite you in the ass lol. Dont fold obviously just play it cautiously. Hopefully you're in position and have a good grasp on your opponents range/style
Mix up your play - don't always play the same cards the same way. People pick up on it and your tricks are useless once people expect them
Try to get an idea of your opponents range of cards, and their style of play.. this helps immensely as the game progresses. If you know someone to be playing a lot of weak aces, make them pay when you get a strong one. Conversely watch out for the guy playing a lot of suited connectors on draw heavy boards. Position is big here.
those are some of the things i've learned, the hard way usually lol. it's good to constantly remind yourself of things like this because it's good practice and good discipline.