Like MJ said the pen tool is by far the best tool to cut images. I always use a 1px feather when playing around with 72 dpi images to get a nice blend on the new background.. More than that I find makes it too blurry around the edges.
Get different brushes to make your backgrouds, just plkay around with them and you can make some pretty neet stuff.
I try to avoid the filter effects in photoshop because I prefer to make them myself and have better control over the effect.
Like Toxic said, always hold down the shift key when resizing images because nothing ruins a sig faster than out of proportion fighter.
You basically have to make a ton of sigs and youll definatly get the hang of it. Your sigs already look good, cant wait to see the way you progress.
Hope this helps!