There is a period of time from when an employer decides they need to employ someone and the job being advertised. As a general rule, the larger the company, the longer this period may be. This is because a job role needs to be approved, the job specification created, recruitment costs approved, etc.
Recruitment costs a company a good deal of time, money and effort. The job may not even be advertised if they discover someone who is suitable before they advertise the job.
Let people you know that you are looking for a job. Try and be specific on the type of work you are looking for
Read the local news for announcements of companies moving into the area or planning to expand. Consider contacting them to see if they will be recruiting
Identify companies you would really like to work for. Send in an enquiry letter and make it obvious that you really want to work for them and say why.