How do I make an effective personal statement? Where do I start?

The most important thing is to discard any advice regarding the need to 'stand out' - this results in theatrical and silly statements that overcompensate. Instead, ensure you are simply answering one question - how did your interest in your chosen subject start and how has that developed since? The process is made much easier when students stop thinking of this as a way to sell themselves, and instead a self analysis that articulates their interests for at least 80% of their statement. For example, for students applying to Architecture, they may begin with citing one of the first structures that interested them, delving then largely into a niche i.e. a specific period, materiality, engineering that they like and why. A book, a lecture or simply some online reading about said niche strengthens the statement considerably too.