If you’ve spent any time at a cocktail bar in recent years, you know that bartending can be an art form. There’s nothing quite like watching an experienced professional toss around a cocktail shaker or perfectly dilute your Martini with a strong stir. However, beyond simply being a visual medium, bartending is undoubtedly a scientific craft, and a number of bartenders new to the game can get things seriously wrong. To dig deeper into the most common rookie mistakes made by newbie mixologists, VinePair spoke with Greg Innocent, beverage director of Chicago’s Parker Restaurant Group, to learn more.

The most common rookie mistake according to Innocent? Incorrect scooping of bar ice. “I see this happen with bartenders and, honestly, with servers a lot — scooping up their ice with glass shakers or glass cups,” he says. “Glass should absolutely never enter the ice well.” Scooping ice directly with a cocktail shaker or a serving glass is not only unsanitary, as your hands are entering the same container storing things that will then be used in guests’ drinks, but you also run the risk of glass shattering while submerged in the ice. “If that glass breaks in the ice bin, you now have to burn all of that ice off, which sets service back significantly,” Innocent explains. “It’s really, really important that people are taking the time and proper care to distribute ice with the correct tools.”

Neglecting to use measurement tools is another rookie mistake with potentially disastrous implications. Innocent explains that measuring tools are vital primarily for consistency’s sake, but they’re also crucial for achieving balanced drinks. “There is nothing worse than walking into an establishment and ordering the same cocktail from two different bartenders and being met with a completely different drink each time.” Beyond consistency, Innocent says measuring tools are essential in ensuring a cocktail is balanced. Take, for example, the Espresso Martini. Many bartenders make dozens in a night, but an overconfident approach to the cocktail can lead to it being off balance and even unenjoyable for the consumer. “They’ll use too much sweetener or coffee liqueur, and you end up having a cocktail with a different balance every time it’s ordered,” Innocent says.

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In addition to incorrectly scooping ice and neglecting measurement tools, shaking drinks toward the guest is an additional rookie mistake Innocent observes regularly. “Depending on how hard your shakes are, if that shaker comes out of your hands and slips, it can torpedo and be a complete disaster in your bar,” he says.

Beyond simple, easily adjustable practices, Innocent identifies one rookie mistake that may be a bit harder to correct: overconfidence. He explains that often, bartenders can have a false sense of confidence regarding their guests’ palates, preferring to make the drinks they themselves like rather than getting to know the preferences of the individual guest. “There is a necessary degree of engagement with your guests required for bartenders,” says Innocent, “and it would be a huge mistake on their part to not take the time to understand what the guest sitting in front of them actually wants simply because they think they know best.”

If you’re new to the profession and want to avoid such rookie mistakes, Innocent advises bartenders to put their pride aside. “Think of how you would like to be treated, or how you would like your mom to be treated if she were to walk into this bar,” he says. “You would want someone gentle; someone engaging.” Beyond that, the beverage director also suggests admitting when you don’t know something. “Being humble and having a bit of humility can help you so much,” he says. “Learn from your mistakes, and learn from your team.”