HE WHO WOULD TRAVEL HAPPILY MUST TRAVEL LIGHT.
A N T O I N E D E S A I N T - E X U P É R Y
The build-up to a trip is always exciting, until you get down to the part where you have to stop daydreaming about it and actually prepare for it. Some people are last-minute packers. They can throw a couple of things into a suitcase the night before, or the morning of, a trip and be done with it. I am definitely not one of those people! If you are capable of doing this successfully (and not forget important stuff like cables, chargers and documents), by all means, carry on!
For the rest of us, I think starting to plan out what you want to bring ahead of time will facilitate the process. There are things that you just always have to bring - documents, electronics, personal care goods, underwear, ... - and for these things it is good to have either a checklist (or two: one for short trips, one for longer ones) that you just use on repeat.
Deciding what clothes to pack can be exciting and frustrating at the same time. However, it all boils down to two considerations: How long is your trip? Will you be changing climates?
The basic packing list is based around a one-week trip in a single climate. If you are going on a weekend trip, you should halve the list. If you are going for a month, you should still be taking the same amount as if you were traveling for a week - assuming you have access to a sink and/or laundering facilities. Anywhere in between a weekend trip and a week-long trip is at your discretion. If you are traveling through radically different climates, then it does get a little more complicated, but it is still possible to adapt the packing guides to the situation with a few simple guidelines.
Ideally, everything should fit nicely into a carry-on. Not because you shouldn't ever check your bags, but just to give yourself the flexibility of choosing whether or not you want to check it in any given situation (think speedy exit from airport, or potential layover escape from the airport).
Again, these packing guides are just that: guides. They are by no means definitive lists of things you must bring, but rather a source of inspiration, a starting point for your own packing list.