I make a couple of coffees a day in the Rancilio. I think it is good to get into the habit of cleaning it each time you use it.
Typically I switch off the steam switch wipe off the steam wand straight after use, then turn on the knob to run the pressure down before switching on the water to flush out anything in the wand.
Then I empty the filter and flush out any grinds using the shower head water. Then clean the shower head with a brush or cloth before re-attaching the group and flushing out any further grinds. Then emptying the tray and wiping up any water is a quick clean.
Occasionally, additional cleaning like back flushing (not on your machine) and pulling off the shower head for a clean and if calcium in your water an occasional descale.
I have a small brush for cleaning out the group and steaming wand as well.
This morning I tried one of those "magic erasers" you can get from the supermarket. It is fantastic. You can wipe the filter cup with it and it cleans it up like new. Use it everywhere, no chemicals but pulls off all the dark stains brilliantly.