Whether you have a "top tier" espresso machine for $7K upwards, or you have a lower-priced, lower quality machine, all things being equal, training your barista is perhaps the most important, and most neglected link in the espresso production chain.
Let's assume you are using fresh, properly roasted espresso beans and a good grinder. I know that many establishments can't even manage to do that---but if that's you--STOP! (fresh beans, fresh ground....please).
Training needs to begin with the owner. Either the owner needs to be passionate about his product, and seek professional training OR the owner can hire a professional to come and train their staff. The problem I most often see is that the only training the owner/manager receives is from the salesman/tech they purchased the machine from. They are told, "You just grind it like so, put it in this portafilter here, and smash it with this deal on the side of the grinder..." Really!! This is just like buying a Viking range from your high-end appliance store, and after being told how to adjust the flame, etc---- you are now a master chef! Cool how that works, huh.
Espresso preparation is a culinary art. Those who don't treat it as such produce mediocre espresso on their best day.
'Perfect practice makes perfect' I always say. So before you attempt to call yourself a barista, or call your employees barista--damn well make sure they are trained properly and your espresso will go from being a tone deaf kazoo player to a symphony orchestra.