What is the step-wise best practice for market access?

If you meant a new market "out of your geographical area " I would say partnerships and agencies were created for such thing, and if you meant a new business penetration strategy seriously this will depend on what business we are talking about, the industry, product, culture ...etc all together.
Telecom companies usually goes for a Skimming strategy, top-of-the-pyramid penetration, which is some how considered as a step-wise if not investing heavily in infrastructure.
In a very typical business model, B2B service for instance I would suggest a pilot advertising campaign then measure and forecast, if I am not able to go for a direct qualitative and/or quantitative research.

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