Let's say you don't want to be in business, that's fine; it's not for everyone. In life there's trade offs, the key is to know your options and find what's best for you. If you look around, pay attention to every job you see. The cashier, waiter, salesperson, technician, security guard, manager, nurse, etc; what do you think each of them makes? A manager often makes a middle class income (not always) but there's only 1 in a room full of workers. A nurse may make a middle class income, or not; find out what kind of nurse they are and search the typical income they earn in the region. You'd be amazed how many adults working full time don't earn a decent income. In my state, the minimum wage is $13/hr; but minimum wage jobs minimize the hours their employees get so even that modest sum does not come to them in the expected amount.
I'd say owning your own home (and not having a mortgage that's astronomical), vacationing for at least a week a year, having a reasonable expectation of retirement and earning at least $40k per person in the workforce (if a couple has 2 jobs, then $40k each; if only one works then they'd probably want more than this.) The best advice I can give to those seeking a middle class lifestyle is to go to college or trade school and get a bachelors degree (try to avoid student loan debt.) Owning a duplex (or triplex or 4-plex) can lead to cost savings and improving the odds of being truly middle class by renting out the other unit.
Jobs that often get you into the middle class: UPS driver (100k+ salary with massive benefits), teacher, police officer, nurse, plumber, AC repair, electrician, manager, dental hygienist, utility worker, city worker, Federal government jobs, physician's assistant, chiropractor.
Some jobs pay better or worse depending on the region, small town police sometimes make dismal wages; but most cities pay their police well. Teachers in some states are poorly paid, other states well paid. Some types of nurses get paid poorly compared to other types, make sure not to get the kind of job that pays to little or is in too low of demand.
Some under payed jobs include entry level military (if you want to be in the armed services, you should join ROTC in high school; if you go to college you may start as an officer.) Realtor-you may earn a living as a realtor, or not; most people don't make money at it despite a single sale a month with national average home prices being sufficient to make you middle class. The good thing about realtor commissions, if you make 2.5% of each sale you only need to sell 40 homes to be able to afford your own (other than taxes, increasing prices while saving, living expenese; but at least there is some connection between income and real estate prices.)