Writing about job descriptions and how they should be presented could easily be a topic for a book more than for a simple blog post. There are companies which create very detailed ones, others that are not well structured and in different cases (unfortunately) there are ones which present recipes more than job descriptions. A different thing is about employment agencies; for the fact that they have several clients they tend to include generic job descriptions to attract a high number of candidates for then directing them according to the skills that candidates have; nothing to say about the approach, but then remember to deliver a specific brief to candidates who otherwise will not pass the early stages of the recruiting process!
Going back to your applications, you have to really understand the essence of the job description before applying. I will say something very trivial here about the listed requirements in a job description, but I think I definitely should. When you read a job description the first thing you should do is understanding the requirements more than interpreting that. The list of requirements or skills is related to the ideal candidate researched by a company “right now, right here” not in the future. Then, applying the logic of “becoming the ideal candidate” (through training), it is not a good strategy because we are not talking about career development but about career placement. The first is related to a future state, the latter to a present one. It is true that the job description is something indicative of the ideal candidate and it is normal not being the exact match; but, in terms of the technical skills or experiences needed, you must understand the differences between that ones (the “mandatory”) and the desired ones. If a company is recruiting for a content editor fluent in Italian and Spanish and you know only the latter, thinking about the fact that Italian and Spanish are similar will not help you to get the job. Study Italian before applying! It is true that with training you can improve and get more skills, but depends which ones; that’s why it is so important to understand rather than simply reading a job description. Applying or trying to be interviewed even if you have not the skills can be frustrating for you and for the recruiter.
Therefore the advice? Read and understand the job description without go and to interpret.