This is essentially a question of state management. What are the mechanisms for regulating, managing and ultimately triggering specific states at will. Most states (it could be argued all) are triggered by internal or external events or a combination of both.
Proactively managing state is about recognising which factors trigger specific responses. To start with you have internal dialogue and physiology. Two sides of the 'state coin' - in that each can affect the other. You can use either or both to leverage changes in state.
By the time we reach adulthood we tend to have multiple predictbale responses wired in. They're ready to fire off as soon as they're triggered, it's like walking around a 'state minefield' - you get lots of synasthesia patterns set up see-feel and hear-feel circuits ie. you see something and instantly feel something, you hear something and instantly feel something.
These 'state mines' affect people to varying extents. Some people will find it very difficult to sustain a focused state for very long at all - internal and external distractions are too abundant. Whereas others can already enter states of heightened concentration seemingly at will.
If you want to enhance your ability to enter a state at will the number of ways of attempting this are limited only by your imagination, but successful methods will probably include elements of:
- Cleaning up known existing distractions - identifying the things either in game or out of game - that consistently degrade focus.
- Getting a consistent playspace clear of external distractions.
- Congruently commiting your poker time to just poker - so you're not mulling over work issues in the background. Agree with yourself up front that you are going to play for 3 hours etc. Deal with any internal objections.
- Visualise yourself doing this and successfully entering your preferred state. Step into the visualisation and feel how it feels as your doing it.
- Sensitising yourself to changes in state - so you become more aware of what is stealing your attention
- Practicing managing your physiology and breathing as and when required - this regulates state
Basically state is about focus of attention. Our attention is always shifting - you're simply attempting to marshall it so it can only drift within the confines you set. Sounds trivial but it's a lifetimes work for some people.