There is no single answer to that. In Europe, we have chosen to bring about a high degree of economic convergence before introducing a common currency. In general, each country or region has to decide for itself what the “best way” is. The decision to adopt a single currency is inevitably a political one.
The necessity of a sound and consistent economic policy does not diminish whatever the particular currency or exchange rate arrangement. This becomes obvious when we consider the strenuous efforts that were necessary on the road from the Maastricht Treaty to the establishment of the European System of Central Banks.