To review external factors, what analysis techniques would you recommend for strategic planning?

Dr. Porter's five forces and the threats & opportunities in SWOT analysis.

I also learned about the PESTEL analysis recommended by Tamer in his answer to this question. Conceptually, it provides a structure even to some of the five forces analysis.

This might be a good answer for the members asking about the value of participating in these discussions on Bayt.com.

PESTEL analysis is a great tool