Hi rustyzofkeys! That's great that you're ready to commit to more practice.
I used to practice 3-4 hrs daily when i was growing up, and my teacher always emphasized the following:
1. Don't do it all in one chunk. Take breaks between sessions, or you risk too much muscle tension or even injury.
2. Focused practice is better than aimless long practice. Have an objective in mind.
3. Stretch your hand /fingers (SAFELY) before practice to loosen up and avoid injury.
4. I usually started with 15-30 min of scales / Czerny, then pieces (usually Bach before moving onto classical/romantic/etc pieces I was working on), then finished the day by playing some favorite "older" pieces for review or whatever I wanted for fun (improv, etc). When working on pieces, it's better to work in depth on a small chunk at a time vs playing the entire thing from start to finish aimlessly.
5. The metronome is your friend!
You'll get a lot more out of 3-4 hrs of focused practice broken into sections than 8+ hrs of less focused practice. Diminishing returns definitely kicks in. Focus is key!
Hope this helps, and happy practicing!
