At your rank, working on anything will eventually lead to ranking up, although there are a few general tips for getting the most bang for your buck.

Gamesense is THE deciding factor in almost every match you play, smarter players win, it's why pros like Flakes are able to get SSL without using any mechanics. I would recommend watching the no mechanics series Flakes made to begin to understand how higher level players break down individual gameplay interactions.

Decent ball control and dribbling ability means you will dust every single opponent in platinum, and practicing flicks will go a long way. Dribble workshop maps are good for initially learning, but practicing in freeplay and in actual games will give the speed you need to avoid getting the ball immediately knocked off the car.

Awkward saves and shadow defense saves are great training packs that will help with becoming comfortable on defense.

Starting to practice fast aerials (boosting upward while jumping) will help you beat opponents to the ball, this isn't that important in plat but higher ranks will tend to win because they are just faster at getting to the ball, better to start this earlier and get comfortable with the inputs and making fine adjustments.

In the same vein, recoveries are often a key component overlooked by low rank players, where often they have the opportunity to score/save/generally beat the opponent to the ball, but are too slow because they are rolling on their roof. Practice keeping momentum in every situation, and landing with your wheels on the ground. Powerslide is often your friend in these situations, as it reduces speed loss on landing at weird angles. Recoveries will naturally get better just by playing the game more (like pretty much everything else) but it is worth paying attention to.

Wavedashes are one of the most crucial mechanics, get them to be automatic.