Website speed

Hi,

Can someone perhaps help me out improving the website speed? I am struggling in between a loading speed of 8.5-9.3sec on Pingdom, and lower loading times when I use WPSmush.
I also tried installing JS&CSS script optimizer and CDN Enabler, but don’t understand how both of these work..
I also tried W3cache, which brought down the speed dramatically to 3.75sec, but then the website looked very basic with Times New Roman font, and totally not what it is supposed to look like.. So I deactivated this plugin again.

I’d be happy with a loading speed between 3-4sec. Can anyone help me out by recommending plugins/adjustments/giving tips?

Thanks in advance ??