Make sure that your project preset match your source files specifications(fps, resolution, PAR, etc.).
To know the specifications of your file, you can use the free utility MediaInfo and then make a PrE project with a matching preset.
There shall be not red lines above your clips in timeline.
Also after editing make sure that your render your timeline.
As John says, matching your project settings to your video is vital to a successful editing experience. If you've got a match, you will NOT see red lines above your clips when you add them to your timeline. Is that the case in your project?
Also, AVCHD video often requires at least a quad core or i7 processor with a good load of RAM to edit. If you don't have a powerful, well-tuned system, it could well be that the skipping you're seeing is just your computer unable to process the video data fast enought.
How fast is your processor and how much RAM do you have? What OS are you running?