A key aspect of critical thinking is the ability to discard or change an idea when needed. Often as designers it can be easy to attach oneself to an idea/design concept/etc and as the process moves along it can be difficult to realise that these ideas need to evolve, to develop or to be put to the side. The design process is an evolving path and refinement comes from evaluating ideas and steps along this path and limiting undue emotional attachment certainly helps to move between phases towards a synthesized design.
Critical evaluation requires a variety of methods and sticking to one form of design development limits the understanding of the concepts. Physical models, digital testing, hand drawing, collages, etc are examples of development tools which encourage ideas and an understanding of where the design is at. Evaluating a range of mediums encourages a depth of critical thinking.
A knowledge of what’s happening in the world of architecture is also essential, by viewing architectural examples the brain learns to review and builds a subconscious library of design examples which will help to generate ideas for your own projects.
There are many considerations and influencing factors within the design process and this obviously creates something of a “juggling act”. A designer must respond to these factors appropriately and an example of this is logic versus creativity. Too much logical thought and the design may became stale and ideas difficult to generate while too much creativity may compromise functional requirements. Critical thinking is the ability to weigh up the effects and needs of the different factors involved. Ultimately the concept of critical thinking is a broad one and the best way to effectively apply it is through continual practice. Each person will have differing opinions and it is advisable for everybody to find their own methods for critically evaluating their designs. An example that I have used is a physical model to test shadow effects for a facade idea: