There are 2 things that you could do that works well in trying to learn how to play in every key
1. take a simple basic song and play it in every key.
2. take songs you already know and play it in the original key 1 key higher and 1 key lower.
Number 2 i started doing when people at my church would just start singing songs out the blue and it seemed like they were always 1 key sharp or flat of the original key. So i just started learning songs in original ,sharp, and flat to cover all my basis.
that grew me alot.
Number 1 i started doing when my mind was able to handle that much practice in 1 session. The worst thing you could do is set these unrealistic practice regimens and then get discouraged in your practice because it to much all at once or just flat out boring.
I hope this helps.
Choirlist.com has piano tutorials on songs
