Apply the ‘Prime the Pump’ principle
In the prime the pump principle you look at the feature list of future iterations of an agile project. This looking ahead will help you plan for future architecture implications of the project. When the development team actually reaches one of the future iterations, you as the architect would have made your architecture decisions.
Just enough architecture
As an architect you want to ensure that all architecture pieces are in place before handing it off to the developers; however in an agile project you usually do not have this luxury. The key is to develop an architecture that is enough to get the developers moving. You can take advantage of the iterative nature of agile by knowing you will review /update your initial architecture.
Wear multiple hats
Don’t just be an architect on an agile project. Get your hands wet by writing some code, setting up infrastructure or even playing the role as P.M