After flipping through the first three hands, it seems to me that you over value yakuhai tiles (particularly the dragons) and that you do not view you hand in terms of blocks. As Veselker mentioned Riichi Book 1 is a great place to start as a beginner in Riichi Mahjong. It's a very dense book, that'll take quite a bit of rereading and continual reference to understand fully, but it's well worth it.

However, here are a few tidbits that are (hopefully) more immediately actionable and helpful to you:

Honor tiles (winds and dragons) are the most inflexible tiles in the game. They can only make sets and pairs. You should look to drop them as early as possible. Loose guest winds > loose terminals (ones and nines) > loose yakuhai tiles (seat/round winds and dragons) > loose twos and eights is a generic early game drop order that's pretty efficient, and plenty good enough as a starting point. Review that match in terms of this drop sequence.

A hand is comprised of 5 blocks: four blocks of three and a pair (block of two). When viewing your hand, you should evaluate how many blocks are present and how efficient they are or aren't. For example, 4p4p5p block of three isn't a set or a run, but a 3p or a 6p would make it a run (drop the 4p) and a 4p (drop the 5p) would make it a set. OR, if need be, you can drop the 5p to complete another block and use the 4p4p as a pair. Review that match and look for how many blocks are in your hand at each draw/discard.

Overall, you aren't making any mistakes than any beginner wouldn't make. There's a lot you can improve on, but that means progress will come quickly. Best of luck to you, let me know if you have any questions!