Be sure to double check your specific airline's baggage requirements before checking in. In the past, airlines had more rigid standards about what length, width and height were allowed. Now many American carriers only specify a maximum "linear inches" measurement, which refers to the added length, width and height. This allows passengers to bring a wide variety of bags on board that may use packing space more efficiently or meet various packing needs better.
Once you know your baggage size limitations, consider what kind of bag will work best for your trip. A soft-sided duffel bag can often pack in a lot of clothing, especially if it includes an expander, but it may not be right for fragile items or those individuals who are physically unable to carry a heavy bag. Hard-sided roller luggage is an easy-to-carry alternative that might keep your clothes wrinkle-free but also might be harder to efficiently pack.
Most airlines permit a large carry-on bag that fits their sizing requirements and also a smaller "personal item" that can fit under a seat. You can use this allowance to give yourself some more space for necessary items when packing. The personal item could be as small as a purse, but backpacks and totes are also permitted. Carry a larger tote that can hold various accessories or toiletries, and you can save more space for clothing in your carry-on luggage.
Even if you're flying on a small regional jet, don't be afraid to pack the maximum sized carry-on bag. You are entitled to a valet or gate check option when boarding the plane on smaller sized aircraft. This is a free service that stows larger carry-on bags with checked luggage, but you are able to check and retrieve your bag immediately in the jet way. This is a convenient service that saves you worry about whether your carry-on will fit in overhead bins.
