There are several trends you can follow. You have the trends developing in your area of expertise, trends in the job market and other developments. You can keep track of each trend area in different ways.
Sign up for newsletters on websites where there is a lot of talk about your profession. Many websites use guest bloggers who are well positioned in their market. You can absorb a lot of information quickly by reading interesting articles from newsletters. By specialty, there are also blogs and forums that deal with the latest developments in your field. For example, for IT this is Computable and for SEO experts SearchEngineWatch. Here you can discuss with your peers and gain knowledge.
To follow trends in the ZP market, you can use websites that analyze statistical data. Consider websites that specialize in numbers for Independent Professionals such as ZP Facts. For more substantive pieces on the ZP market, you can check out ZiPconomy. And furthermore, you can also use the Central Bureau of Statistics.
You should not only focus on your own area and market, your sales techniques and cultural changes are also important. For example, by keeping up with SocialMediaExaminer, you learn new techniques for applying media to your business to get leads. Cultural changes you keep up with by keeping up with the news and occasionally reading the newspaper so you can better target your audience.