Inner game is what is going on in your mind and body.
Outer game is your behaviour and the actions you take.
Both influence each other. Part of the ‘Be, Do, Have’ cycle.
Work on improving both. But remember to keep things simple.
Most results come from the simple things.
As far as inner game goes: being present, not talking shit about yourself, feeling good in your body, working towards goals or improving yourself, not taking things personally.