There are many ways that you can improve your piano playing. Some of then are quite simple and straightforward while others take some time and effort to make a difference. Here is just some random ideas about potentially useful tools you can use.
I have briefly mentioned this one before but a metronome can be a really useful tool. It can be used to check whether a piece is fast or slow enough, but it can also help with keeping the beat constant. Believe it or not but many piano students have trouble with their timing and just having something external (as opposed to just trying to count in time yourself). The metronome can be a really helpful tool and even though the real mechanical ones are not cheap, you can get an app on your phone that will do the same thing.
Your phone can also enhance your piano playing be recording yourself. Even though you do hear yourself when you practice, you can listen to how you play so much more objectively. Some people would cringe at the thought of recording themselves, it is nevertheless a very useful exercise to record oneself and then listen to it afterwards.
Especially if you are a beginner, having something small and lightweight, such as a coin or eraser to balance on the back of your hands while you are playing, will help you get your wrists up and into the correct position. This positioning is not important because it looks good, but it is important because having your hands in the correct shape will help you with stiffness, soreness and protecting against potential injury. Basically, if you can balance the small object on the back of your hands whilst playing the piano, your hands are in a correct position.
The last useful tool I’d like to mention is having a lead pencil with you when you are practicing. I would recommend either placing it on the music stand or placing it at the end of the keyboard. By having a pencil with you when you are practicing, it means that you can circle sections that need extra work, put in the counting either underneath or on top of the notes. You can also use a pencil to write in the notes that are trickier to read, although I would not recommend writing in all of the notes on the page.
With these few items, that can cost only a very small amount, you can use these items to vastly improve your playing. Give it a try!