The generally held view is that a banner at the top of the webpage is best, as it is seen first, and avoids scrolling down to be seen. (This was particularly important with dial up speeds before broadband became prevalent).
However, another important placement on the webpage has been found on the right hand side, close to the scrolling bar. Here, it is not so important to be close to the top of the page, and so you can often find cheaper advert placements closer to the middle or lower half of the page – useful to know if you’re on a tight budget. It makes sense – people will look at the webpage, and whatever catches their eye, so the top of the page stands out – but they also have to scroll to look through the content of the website. {joscommentenable}
Once you have a web banner – take a look at how to make it work effectively for you - Rapid Banners 
