Also, this might not be the most academic advice, but I find it most important to practice the *music*, not the technical aspect. So, when you can decently play a piece, don't jump to the next one, make it as beautiful as you can. Technique will come with time. 

I only move on if I believe it sounds acceptable.

I've spent 2 weeks on Moonlight Sonata, but I spent the majority as of now learning how to sustain the steady momentum that many people overlook. It's helped me learn how to control myself as I play.

As I improve, so will the previous pieces I've played. That's how I view it.

As with learning anything, practice makes perfect

Before learning how to read sheet music, familiarize yourself with the keys, such as middle C, octaves, sharps/flats

The timing is also important, so if you aren't good with the time or beat, a metronome can be extremely helpful.

To improve speed and muscle memory, scales are really good to practice. Playing a few scales as warm up can be useful, as you begin to learn different keys and the difference with sharps and flats

I would say learning how to read music is like learning a new language. Might be overwhelming at first, but you being to pick up and learn. When learning new songs, try finding the songs in C-major, G-major or F-major as they have either no sharps/flats or only have 1

That's great! :)

There's also never 1 correct way to interpret a piece. One things I absolutely adore about playing myself is finding my own idea of how something should sound. It's good to listen to different versions by great pianists, for inspiration. This is a great channel, for that, they also play several different, very different interpretations of the same piece consecutively. You will notice that first interpretation here really doesn't emphasize the movement that much, but rather the meditative aspect of the piece, the anger and acceptance in the melody. Both are beautiful, in their own, very different ways.

https://www.youtube.com/watch?v=K5-IqJZPxQY

Also, just a heads up - no matter how good you are, you *cannot* expect to learn a harder piece in a week or 2, so don't expect that. I usually spend 3, 4 months before ever playing the pieces I play from beginning to end (2 more, before I do so without major blemishes, at the correct pace). It's just hard work, really. Lots of it.

When you learn a harder piece, it is absolutely crucial that you split it up into many, many segments, which you master individually.