Before you do anything, let your machine fully heat up. I usually turn mine on before getting ready in the morning. Heating the whole group head will result in a more consistent temperature throughout a shot.
Once your machine is preheated, lock in your portafilter as you grind your beans. I have a hand grinder so I find this is a good time to heat the basket. However, if you have an electric grinder or pre-ground coffee, you may want to let it heat for longer. The amount of coffee you need to appropriately fill your basket will depend on your specific machine and basket. For my Gaggia Classic Pro E24 with a 17 - 21g IMS basket, I find 19 grams usually puts my puck at the right height. To find the height for your set up, you want the top of the puck to be just below the shower screen. To check, lock in your portafilter and look at it before pulling the shot. Another complication is that different beans perform best at different grind sizes. This is also affected by how long ago the beans we roasted. With my 1zpresso J-Ultra hand grinder, I start at 1.2.0 and adjust according to taste.
The next step is to prepare your puck. I have issues with channeling that seem to be a result of unlevel grounds. I’ve found that a small fork can help to push the grounds into a more level state, but it’s slow and messy. A proper distribution tool is a necessary long term upgrade if you have this issue. Additionally, a dosing funnel significantly cuts down on the mess while you comb through the coffee. After I am satisfied with the distribution, I tamp with my arm as straight above the portafilter as possible, giving a little twist before pulling up to prevent anything from sticking.
This section applies to unmodified Gaggia Classic Pros. I only do one ‘hack’ when I’m pulling shots, and find that I can get consistently great tasting coffee. I push water through, into a waste cup, until the light turns off. Then when the light comes on, I wait 10 seconds. Finally, I push the steam button to increase the temperature for an additional 5 seconds before starting my shot. More than anything, this is just to get a consistent temperature.
When pulling shots, I rely on an espresso scale for quantitative data points which I later use to improve the coffee. I have gotten the best results pulling shots at about a 2:1 ratio, in about 35 seconds. If you want the best coffee possible, you should be tasting your espresso, as it will provide the most feedback. The general rule is that sour espresso is underextracting and bitter espresso is overextracted. Once you are familiar with how a particular batch of beans pulls, you can look at the time and extraction stream as a measure of the shot’s performance.
After finishing my coffee, I always use some extra water to flush the machine, reducing the build up of grounds in the waterblock/shower screen. I also thoroughly clean my portafilter and basket, and spray air using the included hand pump to clean my grinder. This doesn’t take long and will make future maintenance easier and result in better coffee. Once a week I will take a bit more time to clean my machine with a proper detergent, 5 rounds of 10 seconds on 10 seconds off with a blind basket. And about once every other week, or whenever I get new beans, I will disassemble and fully clean my grinder.