Hey 
@FutureTraineeMaybe  !
That's a really good question, and I completely understand your concerns as there are definitely multiple elements that you are expected to include in your answer. When it comes to these sorts of questions, I would always follow a clear structure to ensure that I address all of the individual elements. Whilst I haven't previously applied to 
Dechert, I have answered a similar question for other law firm applications, and so I thought I would share what worked best for me.
Essentially, the firm is making sure that you:
- Have an understanding of the skills that you possess and how you have developed them
- Know what skills are required for being a commercial solicitor / trainee, and
- Can demonstrate how these particular skills and experiences make Dechert the right firm for you
In terms of the first two elements, I would focus on the skills that are required for a commercial solicitor and highlight those. Whilst there is no set number, I would typically discuss two or three main ones (depending on word count) so that I can go into detail about each. The typical skills that you could potentially discuss are things like proactivity, commercial awareness, communication, client-facing, drafting, and teamwork. 
1. Your Own Skills 
I would start by discussing the skill and how you developed it through your experiences/previous roles - this does not necessarily have to follow the STAR method, as it is more about demonstrating how you have the skill rather than explaining a particular instance in that role. For example, you could discuss how you worked as a committee member in one of your university's societies and how interacting with a wide range of people developed your communication skills. An example of how this might look in practice is:
"In my role as the Welfare Secretary in X Society, when a member was anxious about joining a social event for the first time as they didn’t know anyone, I encouraged them to step out of their comfort zone and reminded them that there would be many people in a similar situation. To make them feel more comfortable, I offered to meet them before the social event so that they wouldn’t have to walk in alone, and introduced them to some of the other new members. This experience developed my confidence and communication skills, as I was required to listen to an individual's situation and communicate a thoughtful solution that was tailored to their problem."
2. Skills of a Commercial Solicitor
I would then relate that to the role of a commercial solicitor/trainee. If you have discussed, for example, a skill in communication, I would discuss how this makes you well-suited for the role as a solicitor / trainee. This could be shown by discussing how you may be interacting with colleagues in the firm, senior members of staff, and clients. You can expand on this to state that you can utilise these communication skills to cater to the audience you are communicating with. This directly relates the skills you have demonstrated you have to what they are looking for, and shows that you have an understanding of the expectations of a commercial solicitor / trainee. An example of this could be:
“I believe that these communication skills make me well suited to the role of a commercial solicitor as I am able to tailor my communication style to whoever I am interacting with in my role, whether this is a supervisor, business support services, or the firm’s clients. This will allow me to develop strong professional relationships with clients and colleagues through adapting to their communication style, such as acknowledging their preference for emails or in-person meetings, and planning accordingly.”
3. How this relates to Dechert
Once you have established this picture of your skillset, it is then important to tie it into the firm itself. This is where you will want to look at the USP's of the firm and how your experiences and skills are best suited for it. For example, if you know that the firm has a unique system, such as a room sharing system, you can discuss how your skills in communication are best suited for this style of working, and how you feel that this system will allow you to make the most out of your training with your colleagues. Essentially, you are discussing 'Why do you want to work at 
Dechert' but linking it to the personal skills and attributes that you possess and how this makes you a good fit. An example of this could be:
"This makes X the right firm for me to train at due to its emphasis on partner approachability and the culture of support amongst trainees. By utilising the firm's room sharing system, I will be able to work collaboratively with those around me and gain meaningful experience early on. This will further develop my communication skills, as I will have the opportunity to interact with a wide range of individuals and learn directly from senior staff, strengthening the quality of my training and working relationships."
This can be a bit trickier with some skills than others, but try to think of why you want to work at 
Dechert, and then think about the skills you will need to do that and how you possess them. This could range from the high-level of responsibility you receive early on, the opportunity to complete an international secondment, or perhaps even their focus in a specific practice area / sector.
I hope that helps! I know that it looks like a lot to fit into one answer, especially if the word count is relatively small, but if you write a couple of sentences for each of the above, it should create a clear structure in your answer and flow together nicely whilst also addressing the whole question. Best of luck with your application 
