I have a wordpress website for my business, with a nice theme on it. That theme references a dozen javascript files, and half a dozen css files. That's obviously a bit slow, and google takes page load speed into account these days, so faster = better rankings.

I'd like to combine and minify all the js files, and all the css files, but when I do that the pages don't load properly. My css slide show disappears, my menu style disappears.

What causes this? Is there any good way to make it work properly? I've resorted to manual trial and error, and i've managed to combine some of the files together, but if I could reduce it even more that'd be good.