Freelancer Icy from icysedgwick.com wrote in to ask, "Is the publishing niche particularly profitable, or would I be better sticking to something like digital marketing?"

For every freelancer, this type of question inevitably crops up: should I write about A or B? Often, one option might seem more interesting ... but another might seem more lucrative.

How can you tell if a particular option is going to make money? And how can you decide whether to follow the money or not?

These aren't straightforward questions, and there will always be examples of freelancers who make money from surprisingly odd topics. I'm going to tackle them here, along with a closer look at the particular niches Icy mentions.

Some topics are inherently more lucrative options than others: normally because there's a large market for products/services related to them. Publications paying for said articles will often be making a fairly large part of their profits from advertising revenue.

So, profitable niches for freelancers include things like:

Obviously, there is one pretty huge caveat here: you need to be able to write about your topic with some degree of authority. I don't mean that you should be an "expert" in it, but you should feel confident that you know what you're talking about. In some niches, it's an advantage to have a related qualification (e.g. you might be a nutritionist writing about diet and healthy eating). 

There are a lot of signs you might look at to see whether or not something is a profitable niche. One very simple one is to look for the presence of very large blogs on that topic (think 50,000 or more readers). Blogs this large aren't likely to exist without money being involved! Large blogs will also often hire freelancers to write for them.

In the digital marketing arena, for instance, there are a lot of large blogs (Copyblogger, Mirasee, Smart Blogger, Convice & Convert, Social Media Examiner, Content Marketing Institute ... to name just a few). 

For publishing, there are several fairly big blogs (The Book Designer, The Creative Penn, Jane Friedman, Rachelle Gardner) ... though none that are as huge as those above, and most cover broader topics than "publishing" alone.

You could also look, though, for other publications – e.g. journals or magazines – devoted to the topic. Do check rates of pay for these: you may well find publications related to a niche subject (e.g. eggcup collecting) ... but they will often pay little or nothing for contributions.

With digital marketing, there are also several big magazines like MarketingWeek, Marketing, MobileMarketing: another good sign. 

Depending on the topic, another good place to look is at companies that might require content on that subject. For instance, if like Icy you're considering writing about digital marketing, you might write for blogs and magazines – but you could also produce custom training materials for businesses to use in-house. Alternatively, you might use your subject knowledge in a direct way by offering to write digital marketing materials (tweets, blog posts, etc) as a ghostwriter for a company.

My rule of thumb as a freelancer has always been that I will not write about something illegal or unethical, or, more simply, I'm not going to write about anything that would make it hard for me to sleep at night! Obviously exactly what you consider "unethical" may not match up with me, but you might consider drawing boundaries around areas like:

Beyond these sorts of areas, though, you may need to weigh up the pros and cons of writing on a particular subject:

Even in the early days of your freelancing career, I'd definitely recommend taking on at least some work because it interests you. If all your assignments are ones that you are only doing for the money, you'll quickly burn out. 

You may also find that, while a topic might not be a hugely lucrative field as a whole, you can carve out your own space within it – especially if you know a lot about it, have a qualification or particular experience related to it, or simply like to keep up with recent developments in the field. 

Ultimately if, like Icy, you're trying to decide between two niches, I'd suggest trying out both for a trial period (e.g. aim to get 3 assignments or aim to write for 2 months on each) to see (a) which you prefer writing about and (b) how the money compares.