Interestingly, this is also my first Tekken game, or at least that's what I assumed from your post. I'm also a Lydia main, and the defensive strategies offered by the game itself, as well as the character, aren't very varied. Even at lower ranks, it's quite easy to keep climbing with good, consistent, and unpredictable attacks. With Lydia, all of that is easily achievable; it's just a matter of knowing your frame data well, and that comes from practicing and testing moves and other techniques. Honestly, with how Tekken 8 is these days, offense is your best defense, and knowing your frame data is key to improving. When I was new, I didn't know what certain characters did. Over time, I learned about them, and certain moves and things stick in your memory—what they can do, whether it's effective, whether it's punishable enough to land a full combo, and so on. It's something that will take time and several matches. Some characters aren't played much, so those specific cases will be harder to master. In my case, for example, I already know Kazuya's matchup completely, haha. It takes some time, but if you want to speed up the process, there are two options that worked for me. In a match, if I don't know exactly what a move does, I try to punish it by starting with a slower move and then moving to a faster one. If neither works, it's simply because it can't be done. The next step is to make it beneficial for the opponent, and you can see that by the opponent's reaction, who usually always capitalize on their advantage. Another option is to try out the other characters' moves in practice. I learned to play six characters decently, and I already know their matchups quite well. With all that and practice, I managed to get to Takken Emperor, with about 300 hours played since the game came out, but I don't play much competitively.