title_body: How can I produce better espresso shots with my Gaggia Classic?
upvoted_answer: The standard parameters of producing a decent espresso is previously discussed here: What are the standard espresso parameters (dose, mass/volume, time, etc.)?
  
  As you can see from this answer, assuming that you have a semi-automatic home type espresso machine, if you want to stick with pre-ground coffee and cannot change the grind size, all you can change is the following three:
  
  
  dose
  time
  tamping
  
  
  Dosage is more or less stable in between 6 to 8 grams. Time is mostly the variable that decides either you produce a spectrum of drinks from ristretto to cafe creme. Thus, you should study on tamping. Illy suggests 20 kgf vertical force. But I assume your home-type machine may not handle such tight pellets. So, try to find the best by experience. (By the way, such devices are designed as 15 bars, but while they are in action they are automatically regulated to 9 bars.)
  
  Some previous discussions on tamping is here:
  
  
  What is essential for a proper tamp?
  How do I know how hard to tamp my coffee?
  How important is tamping coffee for an espresso machine
  All discussions on tamping