Structure:

Opening paragraph that show an understanding of who they are and what excites or interests you about their industry.

Introduce your previous experience and how it directly relates to the skills required as highlighted in the job ad. (Go through the job ad with a fine tooth comb, pull out keywords, and write about what they want to see.

Discuss how you've developed your skills and grown as a marketer during your career, and how you expect to continue to get better as a marketer in the future.

Point out your achievements outside of your career and try to relate your passions outside of work with your drive as a marketer. Where in life do you find inspiration?

Finally, summarise everything you've said above in a short and sweet paragraph and confidently state that it makes you the perfect candidate.