This is a tip I originally heard from Crystal at Money Saving Mom® (it's part of her excellent How to Make Money Blogging series) and I couldn't agree with her more! She puts it so well:
Want to know one of my biggest sidebar advertising pet peeves? When people have a big blank box on the sidebar that, instead of being an ad, says “Advertise Here”.
This screams, “My advertising space isn’t valuable enough for people to want to buy so I instead have this big blank box!” That’s not the message you probably want to convey to potential advertisers.
Update: You may wonder, what you should put in that spot instead? Well, become an affiliate (of maybe Tell Your Time? 
) or an affiliate network and put an affiliate graphic in that spot. I cover all the basics of affiliate marketing in my Affiliate Marketing Explained posts.
Here at BloggingWithAmy you'll find tips, tools & tutorials about blogging and websites. In plain English. Want to 
What's the best way to make an ad that says advertise here? Is it a plug in?
You mean make something like a blog button? Check out this post.
Great tip! I use my affiliate 125×125 banners to fill in when I don't have a paid for ad spot filled (which is quite often LOL!)
This is such a great tip! Thank you! I was planning to work on the side bars of my new site this weekend and would have added a "advertise here" section and now I will look for advertising buttons and beef up my media kit and PR page to invite new advertisers.
Thanks again!
My pleasure!
Just backing Amy up here, The Money Saving Mom series is filled with great information!
This is great advice, don't miss an opportunity to monetize! Great advice once again, oh I also wanted to tell you I installed Sharebar after reading your post about it and I LOVE IT! Thanks for all this awesome info.
Woot!
Thanks, I have a spot open that I haven't got around to filling. I will have to stick something in there.
I've been surprised by how many of those buttons I've seen on what I consider pretty big blogs. So if you DON'T use a button, then what do you do to find an advertiser to fill the spot?
An affiliate graphic! I just updated the post with a link to my Affiliate Marketing Explained post. Thanks for the question!
That link is great! After 4 years of blogging I've finally gotten my feet wet in affiliate marketing this week. It's all a bit overwhelming to me at this point and I'm really nervous that my readers will think I'm spamming them. But we really want my hubby to leave Corporate America so I'm giving this my best shot.
I think I might have asked the wrong question in my earlier comment. What I should have asked is how do you get advertisers in the first place?
Ah, well, you could list your stats on an Advertise page. Also, don't be afraid to approach advertisers and ask them if they'd like to advertise!
Don't know too much about affiliate marketing, but this seems worth looking into.
On occasion, I will fill a blank spot with an ad for a business that I do in exchange for publicity (like displaying my rack cards), instead of traditional payment.
I do this very selectively, though.
How many ads is appropriate? I don't want to overwhelm visitors with ads. I've visited many websites that were covered in ads. I think it deters away from the content and looks spammy. I don't think it says, "You can trust my website." Thoughts.
Ah, hard question. I'm generally a fan of "less is more" but I think some of it depends on your niche. Experiment!
Thanks Amy and Crystal..you ladies Rock! I am really trying some different kinds of advertising..don't know what I like most..but for some reason Google Adsense doesn't seem to work on my site..Hey Amy..Why do you think that is? I have tried everything, but It just won't work…:(
Blessings!