Selecting your ads
Don't think you need to meet all the criteria required by the company to respond to an ad. While employers describe their ideal profile, they don't necessarily expect to find a candidate meeting all the criteria given in the job ad. On the other hand, don't waste your time responding to an ad if the profile is not a good fit with yours. Respond to ads when you largely meet the requirements and fill your weak or missing points by mentioning other strong points in your letter.
If you don't have the qualification asked for, emphasise relevant experience instead
Where a job ad specifies several years' experience and you have much less, respond to the ad anyway, as everyone has to start somewhere