Once you learn the idiosyncrasies of the self checkout lanes, they're invariably faster than staffed lanes, for a few reasons:
1) The queuing is often more intelligent. For normal lanes, you pick a lane and you're stuck there, whereas self checkouts are usually 1 queue per 4 ( or more! ) registers. It's the difference between serial vs parallel. Which is compounded by...
2) Those that prefer the staff registers are invariably slower and unable to handle such new technology as credit cards. When forced to use self checkouts they end up clogging up a register for far longer than they should.
3) Finally; I'm far faster checking myself out than any clerk has ever been.
Meanwhile, all you really need to be aware of while using the self checkout is to START with the bag, and place your items directly in the bag on the scale while scanning. Do not remove any items until you're at the payment screen. That's it.
I far prefer self checkouts, to the extent that it influences which stores I shop at.