The era of getting a free upgrade just by "dressing nice" or being polite is largely over; today, free upgrades are almost exclusively handled by automated loyalty algorithms. Most airlines have a "hierarchy" for complimentary upgrades to First or Business Class. The top of the list is always Elite Status members (Diamond, Platinum, etc.), followed by passengers who hold certain premium airline credit cards. Occasionally, "Operational Upgrades" (Op-Ups) occur if the Economy cabin is overbooked; in these cases, the airline will move a high-status passenger to Business Class to free up a seat in the back. To increase your chances without status, you can check for "last-minute" upgrade offers in the airline app, which aren't free but are often heavily discounted. Another "free" path is to volunteer your seat on an oversold flight; you can often negotiate a Business Class seat on the next available flight as part of your compensation package for taking the delay.