Cocktails should not only taste good, but also look good! Even if a detail like a garnish or an umbrella might seem trivial, it's actually very important and for the cost it has it really improves the perceived value and quality of a drink
Bottled drinks: as usual, you get what you pay for. These mixes (like margarita mix etc) are not high-quality and will end up leaving a bad after-taste that customers notice. You're much better off preparing fresh cocktails and drinks
Experience tells that people act in masses: once you make a drink for a customer, his friends will notice and will probably try the drink themselves (especially if the drink is fun, colorful or trendy), so plan accordingly.
Also, keep in mind that cinemas have a great effect on people, and a new film about James Bond will probably reusurrect a passion for Martini
Vodka should be kept in a freezer since it tastes better cold (keep in mind Russia is cold!)
If you find a good drink and would like to know the recipe, just ask the bartender! They're usually very friendly and will happily tell you their recipe
Plastic toothpicks are better than wooden ones. Wooden toothpicks can splint and float in the drink. The best type is probably a long, plastic toothpick so it can be used to stir and doesn't disappear into the drink
Shaking should be done with a professional shaker. Not with glasses, not with blenders, but with a shaker! It works much better, it's easier to clean, it looks much more professional and it's just the best tool for the job
If you pour some drops on the external side of the glass, don't wipe it but transfer the whole cocktail to a new glass. Wiping it leaves a sticky glass that really turns people off
Your bar should look clean and slick, especially if your customers can see you while mixing. Always wipe your mixing area and wash your tools often: again, this greatly increases the perceived value of your drinks