For your first couple of banners, you've done well.

There are a few ways you can make the render seem smoother and blend into the background better. One is to select everything but the render with the magic wand tool (on the render layer of course) and right click > feather > and make it 3/4/5 pixels, whatever looks good. You may need to do this more than once.

There are plenty of other ways to blend the render in, and to put a banner together in general. Follow a few of the other tutorials on here and try out different techniques, you can only improve!

Another thing I would suggest though, is making a border. I think I explained how to do one in the tut, the easiest way is to just do a 1 pixel black one. (Forget the overlay border layer in the tut if you don't like how it looks). Like you did with your first banner.

I'm glad you guys like the tutorial.