The best way is to just start practicing. I would say pick some simple apps on your (Android) phone and dig straight in.
The great thing about Android applications is that often they generally decompile quite nice into human readable Java so the barrier of entry can be quite low to start reversing.
Grab a copy of JADX[1] - it will decompress and decompile the APK files. If you don't have an Android handset, use an emulator and/or grab APKs from apkpure[2]
Dynamic analysis is a bit more challenging. In my blog post I use Frida[3] extensively.
If you get started on something and get stuck/looking for support, feel free to DM me on Twitter (handle in HN profile), more then happy to help.