Oh!Oh!Oh! Mr Kottah!Mr Kottah! Oh!Oh! Can I answer!
Seriously though, advertising is one of those things that different stuff works for different people.
The most successful advertising is that which is part of your company's over all plan and complements your company's personality.
WOM is often the cheapest, most effective and the only one that many people use.
The upside to WOM is you can be very busy. The down side is growth may be limited or very slow.
What you need to decide is what market you want to serve (or what market you are uniquely able to serve in a way that nobody else can, or is, presently serve) Then you need to speak to them specifically, in thier language, in thier medium.
We use several and WOM is one of our Best. But WOM can only begin when you get that first contact and job.
Yellow pages tho expensive is a critical part of our marketing. It serves to establish that we are in fact a serious player and are here for the long haul.
We also focus a lot of our advertising efforts on the Local Weekly News Papers. Our market demographics indicate that our likley clients are loyal to those papers.
Lastly, we will canvas specific neighborhoods and introduce ourselves.
Face time, and consistenly being in front of your target market are what you are searching for.
A good advertising campaign will grab those with an immediate need and entice them to call you. And,those who have a later need will say "what was that company I saw last month.....Oh, here it is last weeks paper"
Remember, "When People think of trees I want them to think of Mee(s)"

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Repetition is the way people best remember.
A common rule of thumb I have heard over the years is to set your advertising budget to at least 18% of your anticipated sales. That is a ton of money, but it will pay off.
NOTE that is 18% of anticipated (or desired) sales, not 18% of your present sales. You also want to make sure that you make your advertising pushes BEFORE you need the work, not when things slow down. Advertising in the busy season is critical! Don't think that you are too busy to need the ads.
There are lots of good ideas out there on the web on marketing plans, advertising copy and what not. Take time to study them and work hard.
We did this with our current campaign and it took me just shy of 3 months to put it together, but it is working. We are getting serious name recognition now and our calls are really beginning to conform to our service strenghts.
Anyhoo, the last thing you want to do is gather data from your customers to find out how they heard of you, what prompted them to call you and what not. This data is critical to your advertising and business success!
Also, there is a bookelet out there on marketing PHC. can't find it right now as we moved our office but it is an ISA or TCIA or related publication. Has a great marketing section that is priceless. See if you can find it and make use of it.
Gotta Run!