My routine is
Dose to fill the basket
Tap grouphandle to settle grounds
Dose to form a mound
Tap to settle again
Level off using NSEW action
Tamp lightly using just the weight of the tamper
Lightly tap tamper against the side of the gh to loosen grounds caught on the edge of the basket
Tamp firmly and polish the top of the puck by a bit of a twist
Insert into grouphead and pour the shot.
There should be very slight resistance of the puck against the shower screen when inserting.. Its not a good idea to remove the gh before the pour as you may (ie probably will) damage the puck and get channeling
The level of dosing depends on several factors - atmospheric conditions such as humidity being critical.
The grounds will expand when wet so seeing an impression should be normal. Not seeing an impression means underdosing - especially if the extraction is too quick. Channeling (pitting at the sides) means you need to improve distribution. Work on ensuring the edges of the basket are properly filled, especially where the handle meets the filter holder.
If you keep having this problem, and it took me a while to get right, consider investing in a naked gh. It will show you how good/bad your distribution is.