How can i compress my pdfs without using this service (http://smallpdf.com/compress-pdf) and at the same time have the maximum compression possible, like the service above?
I'm not sure how meaningful the term "Maximum compression possible" is. For example, you could drop the resolution of images to 1 dpi, but would you be happy with how they look? Probably not... A lot of it depends on what you're happy with in your final PDF.
Probably the simplest method is to use Preview. Select File>Export and then choose "Reduce File Size" from the Quartz Filters menu.
One of the most effective ways I've found is using pdfToolbox: