Hi Michelle. Welcome to CoffeeSnobs :)
What I used to do before I had a grinder was to ask the person grinding the coffee to please tell me what number/setting the grinder was on. Then next time I would ask them to go up or down a notch, depending on what was needed, until I was happy with what was coming through my espresso machine. This could take a few weeks, depending on how much coffee you drink or are prepared to waste. Also keep in mind that coffee shops use different grinders and they are all callibrated differently so the key is to keep going back to the same place.
30ml of coffee is in fact a standard espresso shot. Many Cafes use a double shot (60ml) as the base for a cappucino, which would be one-third of a 180ml cup. The rest is actually steamed/frothed milk. The aim is for it to take 25-30 seconds for this 30 ml to come out, so were talking strong, concentrated coffee. It shouldnt really be bitter - much depends on the quality and freshness of the beans, the right water temperature, etc - but coffee can taste sour if it gushes through the espresso machine too quickly.
Hope this helps. Every coffee made is an experiment, I reckon. Have fun experimenting and please let us know how you get on.