These 2 questions are 2 faces of the same coin. Do you dread that interview question asking you why they should hire you? Or, what you feel your strengths are?
These questions need you to be clear on the skills and behaviours you find easy and enjoy using; they are also about considering your "fit" for a particular organisation and/or team.
Answering these questions with "I'm hardworking, easy to get along with and a great team player" are not really going to help you stand out against the job hunting competition. Describing how your skills and experience meet the key aspects of the job description, the problems you will be able to solve and your understanding of the company culture/values from the research you have done prior to the interview will help you demonstrate how you will be an asset to the company.
Spending time crafting and practising your response to this type of question will set you apart from the majority of candidates.
Perhaps though you're in the situation of thinking about a new job but you don't really know what you're good at or what you might like to do next. Let alone how you would "sell yourself" to any prospective employer.
My "Discover Your Strengths and Talents" Activity could be just the help you are looking for. 25 self-reflection questions to help you understand what makes you special. Contact me if you'd like a copy: firstname.lastname@example.org