This is your chance to think of all your competencies that are transferrable and how your experience is relevant to the change in careers. For example, if you want to go from a production manager at a publishing company to event planning in the wedding industry, your organisational skills, leadership abilities, etc. are all going to be applicable.
In your refurbished resume, you have to tell the story of your transferable skills to a hiring manager, explaining how qualifications from your previous career are still applicable and relevant. To know this, you must get to know your new industry and gain a sense of the skills that employers require.
Use your resume summary to highlight what type of job you are seeking, but most importantly, with the summary your objective is to sell hiring managers on your candidacy. Use this summary to make it clear how your former career has provided you with the skills you need in your new field, and for this job in particular.