These days you should write your CV in the first person (i.e. I have), rather than the third person (i.e. he/she has). However, you do not need to use "I" in a CV because its use is implied. Do mention things you are good at, but do not go over the top. You can oversell yourself. Don't mention things that you are bad at or say negative things about yourself in your CV.
Make sure that the CV you write conjures up the right image of you and your skills, capabilities and achievements. If you do not match the picture you have painted with your CV at the interview, then your application will not be taken further.
If you are not happy with your CV or you only seem to get rejection letters then please get a professional CV writing service to write it for you. Yes, you will have to pay for it, but it could save you a lot of time, lead to you getting less rejection letters and hopefully it should get you an interview that much quicker. Target your CV toward the position for which you are applying and highlight your accomplishments.
Many companies today use automated applicant tracking systems, where your CV is stored in a database. If you submit two different versions of your CV portraying you in different occupations to the same company then they will most likely be compared, which could cause you to be screened out as a candidate. You could be perceived as unsure of your goals and therefore a hiring risk or, depending upon how different your CVs are, less than forthright.
Since each individual possesses a unique set of talents, skills, abilities, experience, and training, there is no one format best for everyone. Although there are more than a dozen different formats, they are all a variation of 3 basic categories:
In most cases, a chronological CV is benefited by a summary of qualifications that quickly shows relevant skills to an employer.
The functional format presents qualifications that support your current employment objective by focusing on your skills and experiences without showing your work history.
The combination format combines the features of the chronological and the functional formats. It allows you to focus more thoroughly on your marketable skills and qualifications first and foremost before presenting your employment history.