Don't resign without another job. The 'Golden Rule' - don't give up your income without another one sorted. Poverty is not good. You will quickly regret it, panic and get more depressed when you can't pay rent/mortgage/food/bills Desperation is not a good look, applying for jobs.
Sound out friends/previous colleagues. (They may have ideas, jobs going in their place etc. Can fill you in on the requirements of any post advertised, even put in a good word for you.)
Go on a course to help sharpen up your qualifications ( my relative got a job by doing this. By chance one of the interviewers had met her on said course.)
Don't necessarily think you have to fulfil ALL the detailed requirements of the new job. Many / most may well do. Stress them.
Practice what you want to say at interview - your best 3 relevant achievements eg.
Smile, make eye contact with ALL interviewers as you enter the room. (Smile. Very important, they are going to be making up their minds about whether they can get on with you in the first seconds!)
Finally, don't give up too soon. Many years ago I read a research paper on recruitment. Most men keep applying until they get the job/promotion. Most women give up if they don't get the first 3 or so they apply for/are interviewed for. ( Thinking they are just not good enough.)
Did I say 'Smile?'