It probably depends on how badly you need the gigs. If you're brand new and have no exposure, it might be a quick way to get some attention. It also depends on what type of ads you mean though. I wouldn't pay to access advertised jobs. I might pay to post an add locally or something though, or setup an Adwords campaign to bring potential clients to my site and portfolio (I haven't had to do either yet, but on the ad front, those are the options I'd mostly likely consider).
I suppose the best way is to giveaway for free an ebook or something that shows your writing skills. In the ebook you should point to your site where you provide professional service.
As an individual writer I don't think AdWords could be the way to go but advertising on Craigslist and going retro trying printed media (flyers, business cards, classified ads on newspapers and magazines, etc.) may contribute.
I've used AdWords for PR stuff. For me, it's just part of the overall campaign. There are many ways to get your name out there. I don't think limiting yourself is a good avenue to pursue. AdWords (for writers) tends to be more of an image-based ad unless you advertise a specific service (resume, news release, etc). If you use it, make sure to put your name (or company name) in the ad(s).
I usually send in something to the papers. My local rags have an announcement section. So does AdWeek and Luerzer's Archive. But these are pubs that are important to me. There are college alum boards, articles sites you post on regularly and you can post an article about how to do something you do well. I send out a printed newsletter to specific target markets. Basically, it offers a tip sheet or more efficient ways to advertise so their ad dollars aren't wasted but bring in the most ROI. Think about what it is that clients are looking for. That should be the basis of any communication you put out there. Think from the client's point of view. Stand in his/her shoes and think, "Why is hiring sherryk good for me?" It needs to answer that question in some form.
i've found that it helps to be feindly with the people first and see what they like doing if the topics for the jobs if a hobbie and they enjoy doing it that helps me / cause someone who enjoys a topic like webdesign will try his or her's hardest to do a good job.