Some of this information will vary depending on where you are in the world.
In Australia,for example,a popular online site for job searching can be found at; www.seek.com.au. You can even create an account with Seek so that relevant job alerts are emailed to you. Another Aussie one is https://www.careerone.com.au/. A similar site in the UK, for example, can be found at www.jobsite.co.uk.
Many large companies advertise vacancies on their websites. This is especially helpful if you are looking for work in a particular industry or would like to work for a specific company. Search their web sites for a ‘Work for Us’ section.
These agencies can be useful too. They are recruitment specialists so their knowledge of the job scene and the companies hiring staff is often very good. They will need information from you; your work and education backgrounds, your aspirations and preferences, so that they can best serve you. The agencies can assist you with either full time or temporary work. If you are moving overseas to work, it would be wise to register with a few agencies – if possible find those which specialise in your area/s of expertise.
There are sites that are designed specifically to assist your search for government jobs. For example in the USA, https://www.usajobs.gov is the Federal Government'sofficial one-stop source for Federal jobsand employment information. And in Australia the best place to look is https://www.jobs.wa.gov.au/
(Applying for a government job can be a very lengthy process, so make sure you follow the process correctly!).
Some employers still advertise in newspapers although this is not as popular as it used to be.
If you want to get into a specific industry, jobs are often advertised in their publications.
Word of Mouth
Word of mouth is very effective (refer to The Power of Networking). Because word gets around so efficiently be sure not to burn your bridges when you leave a job (even if you found your employer loathsome). Be gracious and positive – your future employer will be wary of stories of conflict and tales of woe.