I think the banners are preety good especially considering that you have only just started doing them. I would suggest looking at the banners you see around yaxay/webhostingtalk etc and see what makes them so special?

You need to use gradients better within the banner, adding more detail to the backgrounds without just sticking to plain colours, quite alot of banners have effects/pictures faded in etc.

The right fonts are crucial, the fonts you are using are very standard..consider downloading some or buying some premium fonts. Fonts can really make the world of difference when it comes to advertising.

Animation is also the next crucial step....test out new techniques and try and apply the animation to attract/lure the customer to your website...flashing "click heres", star shapes that rotate...arrows that move etc.

I think you have done very well so far, you have the basics down. Just keep refering back to other banners and improving your knowledge! The key elements, colour, fonts and high quality images need to be at the front of your mind.

Good Luck!