I'm new to the whole imaging thing myself, however what I have found works well with focus is to use a bahtinov mask to focus on a nearby star. Once I have achieved focus, I then lock the focusser and then slew to the planet (or deep space object for that matter). If im going to use a barlow for imaging, then I make sure the barlow is already in place before focusing with the bahtinov mask.
In Registax you can use the 'wavelets' feature to help counteract the atmospheric effects from poor seeing. plenty here on IIS with experience on using wavelets, also have a look at some of the tutorials on youtube.
