Hi Mark
I'm assuming it only banner ads which you are looking advice with.
We started banner ads a few weeks ago, with mixed success (so far). I would recommend remarketing, it converts well. I would guess there is a little bit of cannibalation going on, but I still think it works (reminds customers of you, and make you look like a big brand)
Because of our industry the categories/topic are usless to us. (In my last job in the furniture industry, we found the categories/topic more useful)
The Keywords are very tricky because you will find you ads appearing on sites that have little to do with you business, just happens to have the word on the page. So far we have not had a conversion yet from keywords, but a free "ad seen and converted". I'm also having problems with analytics's picking up all the banner clicks, but I think its because of a quick bounce (analytic does not even get loaded to record the bounce)
I would start with a very small range of keywords and monitor it closely and use negative keywords and block site that are no good to you (flash game site are the worst for 100% bounce rate).
We started in on region, and once we are happy with the banner campaigns we are going to expand them out (we are already going to expand the remarketing campaign as its working)
Hope this helps
